637 CE
A year defined by the fall of Jerusalem and Ctesiphon to Arab Muslim forces, as the early Islamic conquests swept across the former territories of both the Byzantine and Sassanid empires.
Conflict & Security
- Arab forces besieged Jerusalem, with Caliph Umar ibn al-Khattab reportedly traveling personally to accept the city's surrender from the Patriarch Sophronius. Some sources date the fall of the city to 638 CE.
- The Sassanid capital of Ctesiphon, one of the largest cities in the world, fell to Arab forces after the Battle of al-Qadisiyyah, yielding enormous quantities of treasure to the conquerors.
Geopolitics & Diplomacy
- Caliph Umar's acceptance of Jerusalem's surrender was conducted with notable restraint, with the caliph reportedly guaranteeing the safety of the city's Christian inhabitants and their holy sites.
- The fall of Ctesiphon marked the effective end of Sassanid control over Mesopotamia and signaled the impending collapse of the Persian empire that had endured for over four centuries.
Climate & Environment
- Atmospheric carbon dioxide concentration was approximately 277 parts per million, as later confirmed by ice core analysis.
Culture & Society
- The estimated world population was approximately 210 million.