The Conquests
Syria (13-15 AH / 634-636 CE): The Battle of Yarmouk (15 AH / 636 CE) — one of the decisive battles of world history — routed the Byzantine army. Khalid ibn al-Walid, commanding the Muslim forces, executed a flanking maneuver that destroyed a force estimated at 100,000 against a Muslim force of approximately 25,000-40,000. Syria including Damascus and Jerusalem came under Muslim control. Umar personally traveled to Jerusalem to accept its surrender and signed the Covenant of Umar — guaranteeing the safety of the city’s inhabitants and their churches.
Iraq and Persia: The Battle of al-Qadisiyya (14-15 AH) ended Sasanid Persian control of Iraq. Sa’d ibn Abi Waqqas defeated the Persian general Rustam. Ctesiphon (al-Mada’in), the Persian capital, fell in 16 AH. The final defeat of Persian imperial power at Nihawand (21 AH) opened Iran to Muslim control.
Egypt: ‘Amr ibn al-‘As led the conquest of Egypt (19-20 AH / 640-641 CE), including the Byzantine fortress at Babylon and Alexandria.
Administrative Innovations
The Diwan (diwan): A register of Muslim fighters and their families, entitling them to shares of the imperial revenues. This formalized the relationship between military service and financial support.
The Hijri Calendar: Umar, with the companions’ consultation, established the Islamic lunar calendar dating from the Prophet’s migration (hijra) to Medina — year 1 AH. This provided a shared temporal reference for the community.
The Amsar: Military garrison cities founded as centers of governance and Islamic learning: Kufa and Basra in Iraq, Fustat in Egypt. These became major intellectual centers of classical Islamic civilization.
Umar’s governing principle: He traveled in simple dress, was accessible to complaints against his governors, and established a precedent of accountability — reportedly saying: “By Allah, if a mule stumbled on the banks of the Euphrates from the lack of a road, I would fear that Allah would question me about it.”
See also: Khilafa Rashida, Sahaba, Ali Ibn Abi Talib, Seerah Uthman, Bohra History, Fatimid Caliphate, Din Wa Dawla