Description:On the two-year anniversary of Egypt's uprisings -- teargas and smoke permeate Cairo's Tahrir Square. Police and demonstrators clashed there through the early morning as Egyptians gather in the iconic square, considered the heart of the uprisings that swept former President Hosni Mubarak from power. Protesters now, opposed to President Mohamed Mursi, aim to revive the demands of a revolution that they say has been betrayed by the president and his Islamist allies, the Muslim Brotherhood.(1:20)