In one of the largest crowds to fill the square since the popular uprising that ousted President Hosni Mubarak in February, Salafis chanted for the implementation of strict Islamic law, spurring accusations that they violated an agreement to keep the rally free from divisive issues.
The decision by the Muslim Brotherhood, Egypt's best organized political force, and other Islamist groups to participate significantly boosted the turnout.
These groups stayed away from recent demonstrations seeking to keep up pressure on the military council that took power after Mubarak's fall, leading to smaller crowds.
But the Islamists' participation also highlighted the growing rift between them and liberal activists. Some Islamist groups rallied their members to the square to oppose the adoption of a set of guidelines for drafting a new constitution after parliamentary elections later this year.
Liberal parties endorse the measure in an effort to limit what they fear will be outsized Islamist influence on the new document should religious groups win a large share of the parliament. The Supreme Council of the Armed Forces has accepted the idea.
Islamists oppose it, saying nothing should restrict the right of the new elected parliament to oversee the process of drafting the document. (more)