CAIRO — Egyptian riot police fired tear gas and clashed all day Thursday with dozens of protesters as they tried to tear down a concrete wall built to prevent demonstrators from reaching the Parliament and the Cabinet building in central Cairo. Some in the crowd threw rocks and Molotov cocktails.

The violence came on the eve of the second anniversary of Egypt’s uprising that toppled longtime authoritarian President Hosni Mubarak. Three weeks of mass protests that erupted on Jan. 25, 2011, eventually forced Mubarak out of office.