Oriental Orthodoxy is the second largest Christian denomination in Iraq after the collective Eastern Catholic Churches. It includes the Syriac Orthodox Church, headed by a patriarch in Damascus, and the Armenian Apostolic Church, which serves the population of Armenians in Iraq. A sizable population have fled from Iraq following the US invasion and subsequent conflicts. Most Oriental Orthodox Christians are of ethnic Iraqi-Assyrian heritage, who make up about 500,000. The other significant minority of Oriental Orthodox Christians are ethnic Armenians. Christians are present in Baghdad, Basra, Mosul and northern Iraq.