The Battle of Milvian Bridge was fought in 312 CE between the forces of Constantine and the forces of his rival for political power, Maxentius. It was part of the Civil War of the Tetrarchy. Victory at the Battle of Milvian Bridge allowed Constantine to consolidate his power and ended the rule of the Tetrarchy.

Claudius was the fourth Emperor of Rome. He became emperor following the assassination of Caligula. Claudius was an able administrator and an enthusiastic lawmaker. One of his most notable accomplishments includes leading the Roman conquest of Britain in 43 CE.

Trajan’s Column was built to commemorate the Emperor Trajan’s conquest of Dacia in 106 CE. Dacia had been an independent kingdom (located to the north of Greece) during the early years of the Roman Empire. The barbarian people living in Dacia, however, routinely invaded Roman territory to the south and west, and so they became a target for Roman expansion.

Vespasian was the last of four emperors who ruled during the Year of Four Emperors, following the death of Emperor Nero. Vespasian rose to power in Rome, after leading the suppression of the Judean rebellion in 69 CE. He seized power that same year and ruled as the ninth Roman Emperor until 79 CE.

The paterfamilia was the head of a Roman family. Looking at the roots of the word: pater (father) and familia (family), it becomes clear that the father of a household held this position. The other answers refer to Roman political and military structure.

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.

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.

Claudius came to power in Rome after the assassination of Caligula. Claudius was declared emperor by the praetorian guard in the wake of Caligula’s death. Claudius’ reign is very controversial. Many ancient sources suggest that Claudius was a brutal tyrant, but it is unclear whether this was accurate or slanderous propaganda.

The Marian Reforms were enacted in 107 BCE, during the first consulship of Gaius Marius. The Marian Reforms created a professional standing army and allowed landless peasants to join the army, and even provided them with a consistent wage. The Marian Reforms greatly improved the fighting capacity of the Roman Republic, but had several other consequences. Most notably, the Marian Reforms made it so that armies were loyal to the generals who directed them, rather than to the Republic itself. This contributed directly to the decline of the Roman Republic and the rising power of Roman generals (like Julius Caesar).

Caligula, Claudius, and Nero (in that order) are the last three emperors of the Julio-Claudian Dynasty. Popular history tends to remember all three of them as wicked tyrants and, if the ancient sources are to be believed, with good reason. Seeing as many of the accounts of their rule were written by their rivals or by later politicians who needed to justify their reign, however, the testimony of primary sources is routinely questioned by historians.