(Wikipedia) - In 624 A.D., Heraclius offered peace to Sassanian emperor Khosrau Parviz, threatening otherwise to invade Persia, but Khosrau rejected the offer. On March 25, 624, Heraclius left Constantinople to attack the Persian heartland. To do this, he willingly abandoned any attempt to secure his rear or his communications with the sea, and marched through Armenia and Azerbaijan to assault the core Persian lands directly. He led an army of 40,000. Before journeying to the Caucasus, he recovered Caesarea, in defiance of the earlier letter that Khosrau had sent him.
Heraclius went along the Aras River, destroying Persian-held Dvin, the capital of Armenia, and Nakhjevan. At Ganzaka, Heraclius met Khosrau's army, some 40,000 strong. Using loyal Arabs, he captured and killed some of Khosrau's guards, leading to the disintegration of the Persian army. Heraclius then destroyed the famous fire temple of Takht Soleyman, an important Zoroastrian shrine. Heraclius' raids went as far as the Gayshawan, a residence of Khosrau in Atrpatakan.
Heraclius wintered in Caucasian Albania, gathering forces for the next year. Khosrau was not content to let Heraclius quietly rest in Albania. He sent three armies, commanded by Shahrbaraz, Shahin and Shahraplakan, to try to trap and destroy Heraclius' forces. Shahraplakan retook lands up as far as Siwnik, aiming to capture the mountain passes. Shahrbaraz was sent to block Heraclius' retreat through Caucasian Iberia and Shahin was sent to block the Bitlis Pass. Heraclius, planning to engage the Persian armies separately, spoke to his worried Lazic, Abasgian, and Iberian allies and soldiers, saying: "Do not let the number of our enemies disturb us. For, God willing, one will pursue ten thousand."
Two soldiers who feigned desertion were sent to Shahrbaraz, claiming that the Byzantines were fleeing before Shahin. Due to jealousy between the Persian commanders, Shahrbaraz hurried with his army to take part in the glory of the victory. Heraclius met them at Tigranakert and routed Shahraplakan and Shahin's forces one after the other. Shahin lost his baggage train and Shahraplakan (according to one source) was killed, though he re-appears later. After this victory, Heraclius crossed the Aras River and camped in the plains on the other side. Shahin, with the remnants of both his and Shahraplakan's armies, joined Shahrbaraz in the pursuit of Heraclius, but marshes slowed them down. At Aliovit, Shahrbaraz split his forces, sending some 6,000 troops to ambush Heraclius while the remainder of the troops stayed at Aliovit. Heraclius instead launched a surprise night attack on the Persian main camp in February 625, destroying it. Shahrbaraz only barely escaped, naked and alone, having lost his harem, baggage, and men.