Umar ibn al-Khattab, 634 to 644

Umar turned a fast-growing conquest into a paid, registered and audited state. Most of his tools were new to Arabia. Some were borrowed from Byzantium and Persia.

Why it matters: he built a lean treasury, a paid register and checks on officials, and he built them fast.

• Treasury: Umar set up a central treasury (bayt al-mal) in Medina after consulting his council. Abdullah bin Arqam ran it. Provincial treasuries paid local costs and sent the surplus to Medina. A separate accounts office, modelled on Byzantine practice, recorded all spending. Bayt al-mal
• Defence: in 637 the army became a state department. A register listed every adult man liable to fight, with a fixed pay scale. Pay came at the start of Muharram. Troops posted far away got leave after four months. Reforms of Umar's era
• Soldiers paid in cash, not land: land grants were minor. Soldiers lived on state salaries. Reforms of Umar's era
• Provinces: each conquered area got a governor (amir) and a separate finance officer (amil). Local government was otherwise left largely in place. Rashidun Caliphate
• Garrison cities: Basra, Kufa and Fustat were founded or expanded as provincial capitals.
• Anti-corruption: a department led by Muhammad ibn Maslama investigated complaints against officials. Officials' assets were recorded before appointment and checked every year. Guilty officials were removed. Reforms of Umar's era
• Welfare: zakat and jizya funded the poor, elderly, orphans, widows and disabled. In the famine of 638 the poor got cash and flour. Each orphan got 100 dirhams a year. Bayt al-mal
• ID and data: a census of all Muslim lands and the army register.
• Foreign affairs: the surrender terms for Jerusalem promised Christians protection, freedom of worship, no conversion of churches, and a lighter tax than under Byzantium. Rashidun Caliphate
• Justice: he began codifying Islamic law. He set up the Hijri calendar, dated from 622.
• Succession: a six-man committee chose the next caliph.