Caput Vicesimus Quartus: The Prelude
The Roman government was very concerned about the events on the Roman borders. The Germanic limes was calm for the moment, but on the Danube, the Goths grew larger and larger and seemed to prepare for new invasions. And in the east, the permanently quarreling Parthian rulers had been replaced by the Persian dynasty of the Sassanians, which proved to be the champions of unity, strength and effectiveness.
The first Sassanian King of Kings, Ardashir I, knew the Roman Empire from reports of merchants and from his own journeys to Babylonia. He acknowledged the advantages of Roman meritocracy, bureaucracy and military and worked hard to centralize his own, albeit feudal empire: Even if Ardashir couldn't get rid of the Persian and Parthian magnates, he succeeded in limiting their power as much as possible.
Ardashir's son however, Shapur I, chose a much more dangerous model than Rome: The First Persian Empire, ruled by the Achaemenids. Shapur was obsessed with restoring the old Persian borders in the east (the Indus) as well as in the west (Egypt and Thrace). In the first years of his reign, this seemed to be mere propaganda, and the Roman reponsible were still oonvinced that Shapur would fail because of the noblemen's opposition.
Then came Shapur's eastern campaign against the Kushans, restoring large parts of the ancient Persian Empire. And still, the Romans didn't bother with conflicts between barbarians. Shapur celebrated his triumph in Ecbatana, while his satraps established a working admistration in the eastern territories. He sent the Persian warriors home and made grandiosely empty promises of peace on the western border.
But even if Shapur had wanted peace with the Romans – he was persuaded that his empire could only prosper through expansion, and since all of Persia's wealthy neighboring areas were under Roman control, new conquests would inevitably lead to a conflict between the Sassanian and the Roman Empire. And Shapur was determined to win this struggle and to do what nobody had done before: Overcoming the Roman eagles.
During his youth, Shapur had learned Greek and read the Greek historians dealing with Roman history. He wasn't a particular gifted tactician, but a bookworm and ideologist, a superb writer and a passable orator. He studied the battles of Hannibal and Mithridates; after some point, he was convinced that vanquishing the legions was only a question of mobility, surprise and superior weapons.
On the other side of the Mediterranean, another of Hannibal's mental disciples worked hard to catch up with the superiority of oriental cavalry tactics. In 1015 AUC [1], when Lucius turned 21, he received his letter of recall and boarded a ship for Ostia. Arrived at Rome, he was told that troops from the Rhine border were redeployed on the Danube for an offensive against Gothia.
But this didn't happen. During March 1015 AUC, Persian troops surprisingly crossed the river Eulaios and destroyed the legions of Babylonia and Assyria inferior in numbers. They didn't lay siege to the fortified cities – however, they devastated the hinterlands to endanger the cities' food supply, forcing some minor towns to capitulate even without being under serious military threat. Other cities, mainly populated by orientals without the privileges of colonies, simply defected to the Persians and acclaimed Shapur as their King of Kings.
The First Persian War had begun.
[1] 262 CE