In 602,
the last Byzantine-Sasanian war began; it was the most devastating of the series of wars fought between the two empires. In 618,
Khosrau II sent
Shahrbaraz to conquer
Egypt; one year later the
Sasanians managed to capture
Alexandria, the capital of
Byzantine Egypt. After the fall of Alexandria, the Sasanians gradually extended their rule southwards along the
Nile. By 621, the province was securely in Sasanian hands. Egypt would remain in Sasanian hands for 10 years, run by general Shahrbaraz from Alexandria. As the new Roman emperor,
Heraclius, reversed the tide and defeated Khosrau II, Shahrbaraz was ordered to evacuate the province, but refused. In the end, Heraclius, trying both to recover Egypt and to sow disunion amongst the
Iranians, offered to help Shahrbaraz seize the Sasanian throne for himself. An agreement was reached, and in the spring of 629, the Sasanian troops began leaving Egypt. ==Siege==