ISIS claimed responsibility for Saturday's attack, in which a suicide bomber drove an explosive-laden truck into a building in the busy shopping area of Karrada. The terrorist group said it deliberately targeted Shiite Muslims.
Initial estimates put the death toll at about 125, but by Tuesday that number had risen to 250, according to the Iraqi health ministry. It was the deadliest attack since the U.S.-led invasion in 2003.
The mourners on Wednesday prayed together as a sign of unity and solidarity, rejecting ISIS's sectarian vision of Islam.
"I say to Daesh, every time you bomb a place you make us more united," a young man at the vigil told Reuters, using another name for ISIS.