In 313 C.E. the Roman Empire was divided between those believers of the ancient religious institutions of Rome and the rapidly growing Christian minority. The Roman politicians, in various attempts to garner support, had been systematically persecuting or tolerating Christianity. The Edict of Milan, however, permanently ended persecution of Christianity in Rome and paved the way for the adoption of Christianity as the official religion of the Empire. It was issued by Emperor Constantine.

The First Triumvirate of Rome was a political alliance between Julius Caesar, Marcus Crassus, and Pompeius Magnus. It was not an official political organization, but rather a secretive organization that sought to engineer the downfall of the Roman Republic. Following Crassus’ death the Roman world was essentially in the hands of two men - Pompey (his anglicized name), who controlled the Senate and Julius Caesar who controlled the armies of Gaul and enjoyed the most popular support. When Caesar crossed the Rubicon he was declared an enemy of the state and Pompey was charged by the Roman Senate with defeating him. Thus ended the First Triumvirate of Rome; when Caesar defeated Pompey in battle and then had him assassinated.

The Punic Wars were a series of three wars fought between the Roman and Carthaginian Empires between approximately 265 B.C.E. and 145 B.C.E. At the time of the outbreak of war, the Carthaginian Empire was the largest in the Mediterranean and controlled massive swathes of North Africa and Spain. However, the war would eventually end in their total defeat and ushered in half a millennium of Roman dominance of Europe, North Africa and the Middle East.

As Christianity developed during the first century CE, its earliest followers were persecuted in the Roman Empire. Not until the Edict of Milan in 313 CE was Christianity even legal in the empire. Therefore "the widespread acceptance of Christianity" is the correct answer.

All of the other answer choices were true of Rome during the first century CE as it approached its height in the early second century CE.

Carthage was a powerful city-state in North Africa that fought several wars (called the Punic Wars) with Rome for dominance of the Mediterranean Sea in the third and second centuries BCE. Both Athens and Sparta, two once powerful Greek city-states, had long declined by this point, and were individually never major rivals of Rome. Tyre was a once-powerful Phoenician city that had also declined by this point, due to foreign conquest. Byzantium, a Greek city that would later become Constantinople, was never powerful enough in this period to be a major rival of Rome.

As the Roman Empire expanded through Europe, North Africa, and the Middle East, it came to consist of individuals of a wide variety of religious beliefs. In general, the Roman Empire treated these diverse religious elements with tolerance and a practical acceptance. This changed after the Roman Empire became officially Christian, but as this did not occur until near the downfall of the Roman Empire, it cannot be said to be “generally” indicative of Roman policy.

The Diocletianic Persecution was the last widespread, official persecution of Christians in the Roman Empire. It began in the year 303 C.E. and lasted, in some form or another, until 313 C.E. when Constantine issued the Edict of Milan which officially granted tolerance to practicing Christians within the Empire.

The Roman Emperor held a number of different titles, including pontifex maximus, which is Latin for "chief priest". The title was held by Julius Caesar as a pre-Empire designation, but given to his adopted son Octavian. When Octavian became the first true Roman Emperor with the title Augustus, he kept the designation of pontifex maximus, which was passed on to later emperors.

The common man in the city of Rome during the time of the Roman Empire are generally called “Plebeians,” “Plebs” for short. The term can now carry a connotation of suggesting that someone is ignorant or impoverished.

Christians had long suffered persecution under the rule of the Roman Empire, but the religion continued to grow in prominence and following. In the year 380 C.E. Christianity became the state religion of the Roman Empire following a decree issued by Roman Emperor Theodosius I. Theodosius was inspired by the Nicene Creed (325 C.E.) which was one of the earliest professions of faith in Christianity.