24 May 2017 Last updated at 07:08 BST
Children and adults lit candles, put down flowers and held a minute's silence in tribute, on Tuesday evening.
Events were also held in other cities.
Greater Manchester Chief Constable Ian Hopkins said he was heartened to hear about the acts of kindness from emergency service workers and normal people.
He said: "The people of Greater Manchester showed the people of the world how much we care, how much we care about one another, and how much we care for those in need."
Martin was at the vigil and has more...
Thousands of people have gathered by Manchester Town Hall to remember the victims of Monday night's terror attack at a concert.