The conflict began in April 1992 as part of the break-up of Yugoslavia.
About 100,000 people were killed and nearly half the population forced from their homes in four years of fighting.
Red chairs have filled the street in Sarajevo where the conflict began - 11,541, one for each victim there.
People have been putting flowers on some of the chairs. A teddy bear, toys and schoolbooks were placed on the smaller ones that symbolise the hundreds of children killed during the four-year long siege by Serb forces.
Sarajevans were asked to stop what they were doing at 12:00 GMT for an hour to mark the start of the conflict.