The Battle of Nikiou was a battle between Arab Muslim troops under Amr ibn al-A'as and the Byzantine Empire in Egypt in the spring of 646.
Following their victory at the Battle of Heliopolis in July 640, and the subsequent capitulation of Alexandria in November 641, Arab troops had taken over what was the Roman province of Egypt. The newly-installed Byzantine Emperor Constans II was determined to re-take the land, and ordered a large fleet to carry troops to Alexandria. These troops, under Manuel, landed and took the city from its small Arab garrison towards the end of 645. Amr at the time may have been in Mecca, and was quickly recalled to take command of the Arab forces in Egypt.
The battle took place at the small fortified town of Nikiou, about two-thirds of the way from Alexandria to Fustat, with the Arab forces numbering around 15,000, against a smaller Byzantine force. Despite a hard fight, with one of their champions being slain in single combat, the Arabs prevailed, and the Byzantine forces retreated in disarray back to Alexandria.
Although the Byzantines closed the gates against the pursuing Arabs, the city of Alexandria eventually fell to the Arabs, who stormed the city sometime in the summer of that year. The defeat of Manuel's forces marked the last attempt by the Byzantine Empire to recapture Egypt for some 500 years, with only Emperor Manuel I Komnenos sending an expedition there in the 12th century.
Further reading 
- Charles, R. H. The Chronicle of John, Bishop of Nikiu: Translated from Zotenberg's Ethiopic Text, 1916. Reprinted 2007. Evolution Publishing, ISBN 978-1-889758-87-9. 
- Butler, Alfred J. The Arab Conquest of Egypt and the Last Thirty years of Roman Dominatrix Oxford, 1978.