The powers of an emperor, (his imperium) existed, in theory at least, by virtue of his "tribunician powers" (potestas tribunicia) and his "proconsular powers" (imperium proconsulare). In theory, the tribunician powers (which were similar to those of the Plebeian Tribunes under the old republic) made the emperor's person and office sacrosanct, and gave the emperor authority over Rome's civil government, including the power to preside over and to control the Senate.
The proconsular powers (similar to those of military governors, or Proconsuls, under the old republic) gave him authority over the Roman army. He was also given powers that, under the republic, had been reserved for the Senate and the assemblies, including the right to declare war, to ratify treaties, and to negotiate with foreign leaders.
The emperor also had the authority to carry out a range of duties that had been performed by the censors, including the power to control senate membership. In addition, the emperor controlled the religious institutions, since, as emperor, he was always Pontifex Maximus and a member of each of the four major priesthoods. While these distinctions were clearly defined during the early empire, eventually they were lost, and the emperor's powers became less constitutional and more monarchical.
Realistically, the main support of an emperor's power and authority was the military. Being paid by the imperial treasury, the legionaries also swore an annual military oath of loyalty towards him, called the Sacramentum.
The death of an emperor led to a crucial period of uncertainty and crisis. In theory the senate was entitled to choose the new emperor, but most emperors chose their own successors, usually a close family member. The new emperor had to seek a swift acknowledgement of his new status and authority in order to stabilize the political landscape. No emperor could hope to survive, much less to reign, without the allegiance and loyalty of the Praetorian Guard and of the legions. To secure their loyalty, several emperors paid the donativum, a monetary reward.
While the Roman assemblies continued to meet after the founding of the empire, their powers were all transferred to the Roman Senate, and so senatorial decrees (senatus consulta) acquired the full force of law.
In theory, the emperor and the senate were two equal branches of government, but the actual authority of the senate was negligible and it was largely a vehicle through which the emperor disguised his autocratic powers under a cloak of republicanism. Still prestigious and respected, the Senate was largely a glorified rubber stamp institution which had been stripped of most of its powers, and was largely at the emperor's mercy.
Many emperors showed a certain degree of respect towards this ancient institution, while others were notorious for ridiculing it. During senate meetings, the emperor sat between the two consuls, and usually acted as the presiding officer. Higher ranking senators spoke before lower ranking senators, although the emperor could speak at any time. By the third century, the senate had been reduced to a glorified municipal body.
Senators and equestrians
No emperor could rule the empire without the Senatorial order and the Equestrian order. Most of the more important posts and offices of the government were reserved for the members of these two aristocratic orders. It was from among their ranks that the provincial governors, legion commanders, and similar officials were chosen.
These two classes were hereditary and mostly closed to outsiders. Very successful and favoured individuals could enter, but this was a rare occurrence. The careers of the young aristocrats was influenced by their family connections and the favour of patrons. As important as ability, knowledge, skill, or competence; patronage was considered vital for a successful career and the highest posts and offices required the emperor's favour and trust.
The son of a senator was expected to follow the Cursus honorum, a career ladder, and the more prestigious positions were restricted to senators only. A senator also had to be wealthy; one of the basic requirements was the wealth of 12,000 gold aurei  (about 100 kg of gold), a figure which would later be raised with the passing of centuries.
Below the Senatorial order was the Equestrian order. The requirements and posts reserved for this class, while perhaps not so prestigious, were still very important. Some of the more vital posts, like the governorship of Aegyptus, were even forbidden to the members of the Senatorial order and available only to equestrians.
During and after the civil war, Octavian reduced the huge number of the legions (over 60) to a much more manageable and affordable size (28). Several legions, particularly those with doubtful loyalties, were simply disbanded. Other legions were amalgamated, a fact suggested by the title Gemina (Twin).
In AD 9, Germanic tribes wiped out three full legions in the Battle of the Teutoburg Forest. This disastrous event reduced the number of the legions to 25. The total of the legions would later be increased again and for the next 300 years always be a little above or below 30.
Augustus also created the Praetorian Guard: nine cohorts ostensibly to maintain the public peace which were garrisoned in Italy. Better paid than the legionaries, the Praetorians also served less time; instead of serving the standard 25 years of the legionaries, they retired after 16 years of service.
While the Auxillia (Latin: auxilia = supports) are not as famous as the legionaries, they were of major importance. Unlike the legionaries, the auxilia were recruited from among the non-citizens. Organized in smaller units of roughly cohort strength, they were paid less than the legionaries, and after 25 years of service were rewarded with Roman citizenship, also extended to their sons. According to Tacitus  there were roughly as many auxiliaries as there were legionaries. Since at this time there were 25 legions of around 5,000 men each, the auxilia thus amounted to around 125,000 men, implying approximately 250 auxiliary regiments.
The Roman Navy (Latin: Classis, lit. "fleet") not only aided in the supply and transport of the legions, but also helped in the protection of the frontiers in the rivers Rhine and Danube. Another of its duties was the protection of the very important maritime trade routes against the threat of pirates. Therefore it patrolled the whole of the Mediterranean Sea, parts of the North Atlantic (coasts of Hispania, Gaul, and Britannia), and had also a naval presence in the Black Sea. Nevertheless the army was considered the senior and more prestigious branch.
In the old days of the Republic the governorships of the provinces were traditionally  awarded to members of the Senatorial Order. Augustus' reforms changed this policy.
Augustus created  the Imperial provinces. Most, but not all, of the Imperial provinces were relatively recent conquests and located at the borders. Thereby the overwhelming majority of legions, which were stationed at the frontiers, were under direct Imperial control. Very important was the Imperial province of Aegyptus (modern Egypt), the major breadbasket of the empire, whose grain supply was vital to feed the masses in Rome. It was considered the personal fiefdom of the emperor, and Senators were forbidden to even visit this province. The governor of Aegyptus and the commanders of any legion stationed there were not from the Senatorial Order, but were chosen by the emperor from among the members of the lower Equestrian Order.
The old traditional policy continued largely unchanged in the Senatorial provinces. Due to their location, away from the borders, and to the fact that they were under longer Roman sovereignty and control, these provinces were largely peaceful and stable. Only a single legion was based in a Senatorial province: Legio III Augusta, stationed in the Senatorial province of Africa (modern northern Algeria).
The status of a province was subject to change; it could change from Senatorial towards Imperial, or vice-versa. This happened several times  during Augustus' reign. Another trend was to create new provinces, mostly by dividing older ones, or by expanding the empire.
As the empire expanded, and came to include people from a variety of cultures, the worship of an ever increasing number of deities was tolerated and accepted. The imperial government, and the Romans in general, tended to be very tolerant towards most religions and cults, so long as they did not cause trouble. This could easily be accepted by other faiths as Roman liturgy and ceremonies were frequently tailored to fit local culture and identity.
An individual could attend to both the Roman Gods representing his Roman identity and his own personal faith, which was considered part of his personal identity. There were periodic persecutions of various religions at various points in time, most notably that of Christians. As the historian Edward Gibbon noted, however, most of the recorded histories of Christian persecutions come to us through the Christian church, which had an incentive to exaggerate the degree to which the persecutions occurred. The non-Christian contemporary sources only mention the persecutions passingly and without assigning great importance to them.
In an effort to enhance loyalty, the inhabitants of the empire were called to participate in the Imperial cult to revere (usually deceased) emperors as demigods. Few emperors claimed to be Gods while living, with the few exceptions being emperors who were widely regarded at the time to be insane (such as Caligula). Doing so in the early empire would have risked revealing the shallowness of what the emperor Augustus called the "restored republic" and would have had a decidedly eastern quality to it. It was, for example, his attempt to make himself a god (in the mold of the kings of the Achaemenid Persian Empire, which he had conquered) that helped to turn Alexander the Great's troops against him. Since the tool was mostly one the emperor used to control his subjects, its usefulness was greatest in the chaotic later empire, when the emperors were often Christians and unwilling to participate in the practice.
Usually, an emperor was deified after his death by his successor in an attempt by that successor to enhance his own prestige. This practice can be misunderstood, however, since "deification" was to the ancient world what canonization is to the Christian world. Likewise, the term "God" had a different context in the ancient world. This could be seen during the years of the Roman Republic with religio-political practices such as the disbanding of a senate session if it was believed the Gods disapproved of the session or wished a particular vote. Deification was one of the many honors a dead emperor was entitled to, as the Romans (more than modern societies) placed great prestige on honors and national recognitions.
The importance of the Imperial cult slowly grew, reaching its peak during the Crisis of the Third Century. Especially in the eastern half of the empire imperial cults grew very popular. As such it was one of the major agents of romanization. The central elements of the cult complex were next to a temple; a theatre or amphitheatre for gladiator displays and other games and a public bath complex. Sometimes the imperial cult was added to the cults of an existing temple or celebrated in a special hall in the bath complex.
The seriousness of this belief is unclear. Some Romans ridiculed the notion that a Roman emperor was to be considered a living god, or would even make fun of the deification of an emperor after his death. Seneca the Younger parodied the notion of apotheosis in his only known satire The Pumpkinification of Claudius, in which the clumsy and ill-spoken Claudius is not transformed into a god, but into a pumpkin. In fact, bitter sarcasm was already effected at Claudius' funeral in 54.
Absorption of foreign cults
Since Roman religion did not have a core belief that excluded other religions several foreign gods and cults became popular.
The worship of Cybele was the earliest, introduced from around BC 200. Isis and Osiris were introduced from Egypt a century later. Bacchus and Sol Invictus were quite important and Mithras became very popular with the military. Several of these were Mystery cults. In the first century BC Julius Caesar granted Jews the freedom to worship in Rome as a reward for their help in Alexandria.
Druids were seen as essentially non-Roman: a prescript of Augustus forbade Roman citizens to practice "druidical" rites. Pliny reports  that under Tiberius the druids were suppressed—along with diviners and physicians—by a decree of the Senate, and Claudius forbade their rites completely in AD 54.
While Judaism was largely accepted, it was on occasion subject to (mostly) local persecution.
Until the rebellion in Judea in AD 66, Jews were generally protected. To get around Roman laws banning secret societies and to allow their freedom of worship, Julius Caesar declared Synagogues were colleges. Tiberius  forbade Judaism in Rome but they quickly returned to their former protected status. Claudius expelled Jews from the city however the passage of Suetonius is ambiguous: "Because the Jews at Rome caused continuous disturbances at the instigation of Chrestus he [Claudius] expelled them from the city" . Chrestus has been identified as another form of Christus; the disturbances may have been related to the arrival of the first Christians, and that the Roman authorities, failing to distinguish between the Jews and the early Christians, simply decided to expel them all.
Christianity, originally a Jewish religious sect, emerged in Roman Judea in the first century AD. The religion gradually spread out of Judea, initially establishing major bases in first Antioch, then Alexandria, and over time throughout the Empire. For the first two centuries, the imperial authorities largely viewed Christianity simply as a Jewish sect rather than a distinct religion. Suetonius mentions passingly that: "[during Nero's reign] Punishments were also inflicted on the Christians, a sect professing a new and mischievous religious belief"  but he does not explain for what they were punished.
Tacitus reports that after the Great Fire of Rome in AD 64 some in the population held Nero responsible  and that to diffuse blame, he targeted and blamed the Christians. The war against the Jews during Nero's reign, which so destabilized the empire that it led to the first civil war since the days of Julius Caesar and Mark Antony, as well as Nero's suicide, plausibly provided an additional rationale for persecutions against this 'Jewish' sect.
Persecution of Christians would be a recurring theme in the Empire for the next two centuries. Eusebius and Lactantius document the last great persecution of the Christians under Diocletian at the beginning of the 4th century at the urging of Galerius. This was the most vicious persecution of Christians in the Empire's history. After Diocletian, however, the fact that emperors were often Christians themselves lessened whatever persecutions may have still been occurring.
As the 4th century progressed, Christianity had become so widespread that it became officially tolerated, then promoted (Constantine I), and in 380 established as the Empire's official religion (Theodosius I). By the 5th century Christianity had become the Empire's predominant religion rapidly changing the Empire's identity even as the Western provinces collapsed. This would lead to the persecution of the traditional polytheistic religions that had previously characterized most of the Empire.
The language of Rome before its expansion was Latin, and this became the empire's official language. By the time of the imperial period Latin began evolving into two languages: the 'high' written Classical Latin and the 'low' spoken Vulgar Latin. While Classical Latin remained relatively stable, even through the Middle Ages, Vulgar Latin as with any spoken language was fluid and evolving. Vulgar Latin became the lingua franca in the western provinces, later evolving into the modern Romance languages: Italian, French, Portuguese, Spanish, Romanian, etc. Greek and Classical Latin were considered the languages of literature, scholarship, and education.
Although Latin remained the official and most widely spoken language through to the fall of Rome and for some centuries after in the East, the Greek language was the literary language and sometimes the lingua franca in the Eastern Provinces. With the exception of Carthage, the Romans generally did not attempt to supplant local cultures and languages. It is to their credit that they generally left established customs in place and only gradually supplemented with the typical Roman-style improvements.. Along with Greek, many other languages of different tribes were used but almost without expression in writing.
Greek was already widely spoken in many cities in the east, and as such, the Romans were quite content to retain it as an administrative language there rather than impede bureaucratic efficiency. Hence, two official secretaries served in the Roman Imperial court, one charged with correspondence in Latin and the other with correspondence in Greek for the East. Thus in the Eastern Province, as with all provinces, original languages were retained.
Moreover, the process of hellenisation continued more extensively during the Roman period, for the Romans perpetuated "Hellenistic" culture,[nb 4] but with all the trappings of Roman improvements. This further spreading of "Hellenistic" culture (and therefore language) was largely due to the extensive infrastructure (in the form of entertainment, health, and education amenities, and extensive transportation networks, etc.) put in place by the Romans and their tolerance of, and inclusion of, other cultures, a characteristic which set them apart from the xenophobic nature of the Greeks preceding them.
Since the Roman annexation of Greece in 146 BC, the Greek language gradually obtained a unique place in the Roman world, owing initially to the large number of Greek slaves in Roman households. In Rome itself Greek became the second language of the educated elite. It became the common language in the early Church (as its major centers in the early Christian period were in the East), and the language of scholarship and the arts.
However, due to the presence of other widely spoken languages in the densely populated east, such as Coptic, Syriac, Armenian, Aramaic and Phoenician (which was also extensively spoken in North Africa), Greek never took as strong a hold beyond Asia Minor (some urban enclaves notwithstanding) as Latin eventually did in the west. This is partly evident in the extent to which the derivative languages are spoken today. Like Latin, the language gained a dual nature with the literary language, an Attic Greek variant, existing alongside spoken language, Koine Greek, which evolved into Medieval or Byzantine Greek (Romaic).
By the 4th century AD, Greek no longer held such dominance over Latin in the Church, arts and sciences as it had previously, resulting to a great extent from the growth of the western provinces (reflected, for example, in the publication in the early 5th century AD of the Vulgate Bible, the first officially accepted Latin Bible; before this only Greek translations were accepted). As the Western Empire declined, the number of people who spoke both Greek and Latin declined as well, contributing greatly to the future East–West / Orthodox–Catholic cultural divide in Europe.
Important as both languages were, today the descendants of Latin are widely spoken in many parts of the world, while the Greek dialects are limited mostly to Greece, Cyprus, and small enclaves in Turkey and southern Italy. To some degree this can be attributed to the fact that the western provinces fell mainly to "Latinised" Christian tribes whereas the eastern provinces fell to Muslim Arabs and Turks for whom Greek held less cultural significance.
Life in the Roman Empire revolved around the city of Rome, and its famed seven hills. The city also had several theatres. gymnasiums, and many taverns, baths and brothels. Throughout the territory under Rome's control, residential architecture ranged from very modest houses to country villas, and in the capital city of Rome, to the residences on the elegant Palatine Hill, from which the word "palace" is derived. The vast majority of the population lived in the city centre, packed into apartment blocks.
Most Roman towns and cities had a forum and temples, as did the city of Rome itself. Aqueducts were built to bring water to urban centres and wine and oil were imported from abroad. Landlords generally resided in cities and their estates were left in the care of farm managers. To stimulate a higher labour productivity, many landlords freed a large numbers of slaves. By the time of Augustus, cultured Greek household slaves taught the Roman young (sometimes even the girls). Greek sculptures adorned Hellenistic landscape gardening on the Palatine or in the villas.
Many aspects of Roman culture were taken from the Greeks. In architecture and sculpture, the difference between Greek models and Roman paintings are apparent. The chief Roman contributions to architecture were the arch and the dome.
The centre of the early social structure was the family, which was not only marked by blood relations but also by the legally constructed relation of patria potestas. The Pater familias was the absolute head of the family; he was the master over his wife, his children, the wives of his sons, the nephews, the slaves and the freedmen, disposing of them and of their goods at will, even putting them to death. Originally, only patrician aristocracy enjoyed the privilege of forming familial clans, or gens, as legal entities; later, in the wake of political struggles and warfare, clients were also enlisted. Thus, such plebian gentes were the first formed, imitating their patrician counterparts.
Slavery and slaves were part of the social order; there were slave markets where they could be bought and sold. Many slaves were freed by the masters for services rendered; some slaves could save money to buy their freedom. Generally mutilation and murder of slaves was prohibited by legislation. It is estimated that over 25% of the Roman population was enslaved. Professor Gerhard Rempel from the Western New England College claims that in the city of Rome alone, during the Empire, there were about 400,000 slaves.
The city of Rome had a place called the Campus Martius ("Field of Mars"), which was a sort of drill ground for Roman soldiers. Later, the Campus became Rome’s track and field playground. In the campus, the youth assembled to play and exercise, which included jumping, wrestling, boxing and racing. Riding, throwing, and swimming were also preferred physical activities.
In the countryside, pastime also included fishing and hunting. Board games played in Rome included Dice (Tesserae or Tali), Roman Chess (Latrunculi), Roman Checkers (Calculi), Tic-tac-toe (Terni Lapilli), and Ludus duodecim scriptorum and Tabula, predecessors of backgammon. There were several other activities to keep people engaged like chariot races, musical and theatrical performances,
Clothing, dining, and the arts
The cloth and the dress distinguished one class of people from the other class. The tunic worn by plebeians (common people) like shepherds and slaves was made from coarse and dark material, whereas the tunic worn by patricians was of linen or white wool. A magistrate would wear the tunic augusticlavi; senators wore a tunic with broad stripes, called tunica laticlavi. Military tunics were shorter than the ones worn by civilians. Boys, up until the festival of Liberalia, wore the toga praetexta, which was a toga with a crimson or purple border. The toga virilis, (or toga pura) was worn by men over the age of 16 to signify their citizenship in Rome.
The toga picta was worn by triumphant generals and had embroidery of their skill on the battlefield. The toga pulla was worn when in mourning. Even footwear indicated a person’s social status. Patricians wore red and orange sandal, senators had brown footwear, consuls had white shoes, and soldiers wore heavy boots. Men typically wore a toga, and women a stola. The woman's stola looked different than a toga, and was usually brightly coloured. The Romans also invented socks for those soldiers required to fight on the northern frontiers, sometimes worn in sandals.
Romans had simple food habits. Staple food was simple, generally consumed at around 11 o’clock, and consisted of bread, salad, cheese, fruits, nuts, and cold meat left over from the dinner the night before. The Roman poet, Horace mentions another Roman favourite, the olive, in reference to his own diet, which he describes as very simple: "As for me, olives, endives, and smooth mallows provide sustenance." The family ate together, sitting on stools around a table. Fingers were used to eat solid foods and spoons were used for soups.
Wine was considered a staple drink, consumed at all meals and occasions by all classes and was quite cheap. Many types of drinks involving grapes and honey were consumed as well. Drinking on an empty stomach was regarded as boorish and a sure sign for alcoholism, whose debilitating physical and psychological effects were known to the Romans. An accurate accusation of being an alcoholic was an effective way to discredit political rivals.
Roman literature was from its very inception influenced heavily by Greek authors. Some of the earliest works we possess are of historical epics telling the early military history of Rome. As the empire expanded, authors began to produce poetry, comedy, history, and tragedy. Virgil represents the pinnacle of Roman epic poetry. His Aeneid tells the story of flight of Aeneas from Troy and his settlement of the city that would become Rome. Lucretius, in his On the Nature of Things, attempted to explicate science in an epic poem. The genre of satire was common in Rome, and satires were written by, among others, Juvenal and Persius. Many Roman homes were decorated with landscapes by Greek artists. Portrait sculpture during the period utilized youthful and classical proportions, evolving later into a mixture of realism and idealism. Advancements were also made in relief sculptures, often depicting Roman victories.
Music was a major part of everyday life. The word itself derives from Greek μουσική (mousike), "(art) of the Muses". Many private and public events were accompanied by music, ranging from nightly dining to military parades and manoeuvres. In a discussion of any ancient music, however, non-specialists and even many musicians have to be reminded that much of what makes our modern music familiar to us is the result of developments only within the last 1,000 years; thus, our ideas of melody, scales, harmony, and even the instruments we use would not be familiar to Romans who made and listened to music many centuries earlier.
Over time, Roman architecture was modified as their urban requirements changed, and the civil engineering and building construction technology became developed and refined. The Roman concrete has remained a riddle, and even after more than 2,000 years some Roman structures still stand magnificently. The architectural style of the capital city was emulated by other urban centres under Roman control and influence.
Following various military conquests in the Greek East, Romans adapted a number of Greek educational precepts to their own fledgling system. Home was often the learning centre, where children were taught Roman law, customs, and physical training to prepare the boys to grow as Roman citizens and for eventual recruitment into the army. Conforming to discipline was a point of great emphasis. Girls generally received instruction from their mothers in the art of spinning, weaving, and sewing.
Education began at the age of around six, and in the next six to seven years, boys and girls were expected to learn the basics of reading, writing and counting. By the age of twelve, they would be learning Latin, Greek, grammar and literature, followed by training for public speaking. Oratory was an art to be practised and learnt, and good orators commanded respect. To become an effective orator was one of the objectives of education and learning. In some cases, services of gifted slaves were utilized for imparting education.
The imperial government was, as all governments, interested in the issue and control of the currency in circulation. To mint coins was a political act: the image of the ruling emperor appeared on most issues, and coins were a means of showing his image throughout the empire. Also featured were predecessors, empresses, other family members, and heirs apparent. By issuing coins with the image of an heir his legitimacy and future succession was proclaimed and reinforced. Political messages and imperial propaganda such as proclamations of victory and acknowledgements of loyalty also appeared in certain issues.
Legally only the emperor and the Senate had the authority to mint coins inside the empire. However the authority of the Senate was mainly in name only. In general, the imperial government issued gold and silver coins while the Senate issued bronze coins marked by the legend "SC", short for Senatus Consulto "by decree of the Senate". However, bronze coinage could be struck without this legend. Some Greek cities were allowed to mint  bronze and certain silver coins, which today are known as Greek Imperials (also Roman Colonials or Roman Provincials). The imperial mints were under the control of a chief financial minister, and the provincial mints were under the control of the imperial provincial procurators. The Senatorial mints were governed by officials of the Senatorial treasury.
In recent years, question relating to ancient demographics have received increasingly more scholarly attention, with estimates of the population size of the Roman empire at its demographic peak now varying between 60-70 million ("low count") and over 100 million ("high count"). Even by adhering to the more traditional value of 55 million inhabitants, the Roman Empire constituted the most populous Western political unity until the mid-19th century and on a global scale probably until around AD 1000.