The procedure for the nomination and appointment of a Roman monarch was quite convoluted. First, the Senate had to choose a candidate for the monarchy. Then, that monarch needed to get the support of the people. Next, he had to court the approval of the Curiate Assembly. Finally, a would-be monarch needed religious approval and the reaffirmed support of the Senate. Only after all this would a ruler have the title of imperium conferred upon him and become king.

While Constantine did in face craft the Edict of Milan he never moved the seat of government there, so that city would not be a good choice. Gaul was the Roman province containing modern-day France, Switzerland, and Luxembourg, not a city at all, so it would not be a good choice. Budapest while occupied by the Romans for a time, was never their seat of government, so that would not be a good choice. Baghdad, while an ancient city in its own right, was never a Roman governmental seat either, so it too would not be a good choice. Lastly, Istanbul was renamed Constantinople after Constantine the Great moved the seat of the Roman Empire there, so Constantinople would the best choice.

A republic is a system of government in which people elect representatives to enact laws on their behalf. It is distinct from direct democracy in that the people do not actually get to vote on issues themselves, but instead appoint representatives. It was the political system which prevailed in Rome from 507 BCE until the rise of the Roman Empire in 27 BCE. It is also the political system which prevails in the modern United States of America.

The Law of Twelve Tables was the first codified legal code in the history of the Roman Republic. It was enacted in 450 BCE. The Twelve Tables were designed to protect the rights of all citizens of Rome and to try and minimize conflict between the patricians and the plebeians.

Augustus Caesar was the first emperor of the Roman Empire. He came to power in 31 BCE (as Octavian) and was crowned Emperor Augustus Caesar in 27 BCE. His reign marks the beginning of the Pax Romana — a two centuries long period of prolonged peace and prosperity in the Roman Empire. He created a standing army and introduced a pension for Roman soldiers (two reforms which greatly improved the fighting capacity of the Roman Empire). He was not, however, assassinated by a group of noblemen (that was Julius Caesar).

Proconsuls, in the Roman Empire (and also the Roman Republic) were effectively governors. They were rulers chosen to administer a certain province within the Roman Empire. Julius Caesar was notably the proconsul of Gaul after he conquered this territory in the Gallic Wars.

Nero’s death in 68 CE brought to an end the rule of the Julio-Claudia Dynasty, which had begun with the reign of the first Roman Emperor, Augustus Caesar. Nero’s death also ushered in the Year of the Four Emperors. The year 69 CE witnessed the first civil war in Roman history since the conflict between Octavian and Mark Antony (which brought to an end the Roman Republic). The Year of the Four Emperors ended with the Emperor Vespasian taking control and ushering in the Flavian Dynasty.

A consul was the highest elected official in the Roman Republic. Generally speaking two consuls were elected at the same time, to serve concurrently for a term of one year. Consuls had extensive administrative, legislative, and executive powers.

In the early years of the Roman Republic, it was common for poor plebeians to be enslaved by patricians if they accumulated significant debts. This debt slavery was abolished in 450 BCE with the codification of Roman law through the Twelve Tables.

Vespasian, who came to power at the end of the Year of Four Emperors, was the first Emperor of the Flavian Dynasty. He was also the first Emperor to be succeeded by one of his sons. Titus, who took power in 79 CE, was Vespasian’s son. Both Vespasian and his son Titus gained political prominence through the suppression of the Judean rebellion.