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In 636, Caliph Umar had re-invaded Iraq, after a previous Muslim army was defeated and removed from the region. The Sasanian and Arab armies met at the village of Qadisiyyah, southwest of the modern city of Hilla in Iraq, which is near ancient Babylon. The battle was mostly fought by a relatively inexperienced Arab army against ; however, much of the Persian army was also inexperienced, as many of their best troops had died or were depleted from previous engagements. This made the better trained two sides relatively even and equipped Persiansafter the first day of the battle it did not seem that either of them could break each other's defenses. However, a A key turning point was Arab reinforcements to that strengthened the ArabsIslamic army, who were much more professional soldiersand well trained, and that arrived at the battle of Qadisiyyah on the second day. These numbered about 5000 and proved to be the difference in allowing the Arabs to breakthrough the Persian main line, causing them to routed and forcing the main Persian force to retreat. By the fourth day of the battle, the outcome was clear and the Sasnian army fled to the north, although many were killed as they attempted to flee. The key outcome came after the battle. First, a large amount of booty was captured from the Sasanian army. This helped finance later battles and the Muslim army to further march north. The next major defeat for the Sasanians was at their capital Ctesiphon, where their capital was captured after a two month siege. In 650, a new phase of invasions was then ready, leading to the conquest of Persia and defeat of the Sasanian Empire.