The first shells hit Zagreb at 10.23 hours on May 2, 1995.
The shelling continued the next day, hitting a children's hospital, a pensioners' home, and the Croatian National Theatre.
Six people were killed and 205 were wounded, including 39 gravely.
The attack was the rebel Serbs' retaliation for a defeat in western Slavonia, which their leader at the time, Milan Martic, admitted in front of TV cameras. The Hague war crimes tribunal sentenced him to 35 years' imprisonment for the shelling of Zagreb.
A square in the capital was named after the victims in 2007.