The Battle of Dara was fought between the Eastern Roman Empire and the Sasanians in 530 AD. It was one of the battles of the Iberian War.
Procopius's account of this engagement is among the most detailed descriptions of a late Roman battle.
Background
The Byzantine Empire was at war with the Saanians from 527, supposedly because Kavadh I had tried to force the Iberians to become Zoroastrians. The Iberian king fled from Kavadh, but Kavadh tried to make peace with the Byzantines, and attempted to have Justin I adopt his son Khosrau. Justin agreed, but on the terms that he would do so only in a rite reserved for barbarians. This failed to satisfy Kavadh, who attacked Byzantine allies, so Justin sent his generals Sittas and Belisarius into Persia, where they were initially defeated. In 529, the failed negotiations of Justin's successor Justinian prompted a Sasanian expedition of 40,000 men towards Dara. The next year, Belisarius was sent back to the region alongside Hermogenes and an army; Kavadh answered with another 10,000 troops under the general Perozes, who set up camp about five kilometers away at Ammodius, in the near vicinity of Dara.
Deployment
The Persians, outnumbering the Romans by 15,000 men, deployed around 20 stades away from the town of Daras and drew up their battle lines. Despite being outnumbered, Belisarius decided to give battle. He dug a number of ditches to block the Persian cavalry, leaving gaps between them to allow a counterattack. According to Irfan Shahid, the tactic was adopted from the Persians at the Battle of Thannuris two years earlier. These were pushed forward on either flank of his position, while his center was refused back. Here he placed his unreliable infantry behind the center ditch, being placed close enough to the walls of the fortress to provide supporting fire from the city battlements. On the left and right flanks were the Byzantine cavalry, of questionable quality. Supporting them on their interior flanks were small bodies of Huns: 300 Hun cavalry under Sunicas and Aigan supporting the left; and as many more Huns on the right under Simmas and Ascan. Belisarius also placed a body of Heruli cavalry under Pharas in ambush position off his left flank. A reserve composed of his own bucellarii household cavalry was held behind his center and commanded by John the Armenian, his trusted lieutenant and boyhood friend.
Battle
On the first day, according to Procopius, there was no general engagement, but instead a series of challenge fights between champions of both sides. One particular combat involved a Persian knight, who challenged Belisarius to single combat; but was instead met by a Byzantine bath slave named Andreas. Andreas, who had been secretly training with Belisarius' own household troopers, killed not only this Persian champion, but also a second challenger later in the day. The Persians then withdrew to Ammodius for the night. Some authors, however, have expressed doubt as to the pure historicity of Procopius' account and state that while instances of single combat did likely occur during the course of the battle, Procopius' description is intended to be a narrative device rather than a factual account. Another source, believed to be based on official documents, does indeed reference individual combat, but makes no mention of Andreas and, furthermore, places any single combat engagements at a different stage of the battle.
After the first day of skirmishes, Belisarius sent a letter to the Persian commander. Rather than fight a battle, he believed it was best to avoid conflict and instead insisted that their disputes be settled by discussion. The letter read, "The first blessing is peace, as is agreed by all men who have even a small share of reason. ... The best general, therefore, is that one which is able to bring about peace from war." The letter either fell on deaf ears or Perozes already wanted to negotiate which eventually failed, the battle resumed. The Persians already thought of the Byzantine army as a second-rate army; this letter, along with his numerical superiority, likely made Perozes even more confident of victory. In his book on Belisarius Brogna merely says that Belisarius sent the letter because of his good moral character. Mahon claims in his book that Belisarius doubted his chance of victory and this is why he sent the letter.