Hundreds of thousands of Lebanese waving flags, some carrying anti-Syrian banners, massed in Martyr's square in Beirut on Tuesday to commemorate the first anniversary of the assassination of former Premier Rafik Hariri.
The gathering answered a call by groups opposed to Syrian involvement in lebanon aiming to show their popular strength amid deep political divisions.
Syria's troops left Lebanon in April under international pressure after nearly 30 years, and a UN probe into Hariri's murder has already implicated top Syrian and allied Lebanese security officials. Damasmcus refutes any involvement.
Rafik Hariri's sister Bahia Hariri prayed at his graveside next to the square.
Outside some demonstrators carried signs calling for "The Truth" and shouted the name of Hariri's son and political heir, Saad Hariri, whilst others carried placards critical of Syria and its president, Bashar Assad.
Thousands of troops and policemen, backed by armoured vehicles, sealed off Beirut's downtown area to provide security and guarded approaches to the city.
The government gave schools the day off and businesses closed.
The demonstration was expected to climax shortly after midday - the time when a huge truck bomb exploded on a downtown seaside street as his motorcade drove by a year ago, killing him and 20 others.
The main pro-Syrian Shiite Muslim groups, Hezbollah and Amal, were not taking part in the demonstration, which was expected to be largely dominated by Sunni Muslims from Hariri's sect and by Christian and Druse allies.
Amal is holding its own commemoration later Tuesday in southern Lebanon. Amal and Hezbollah, who are represented in the Cabinet, have been locked in a power struggle with the government's majority led by the Saad Hariri bloc.
The groups leading Tuesday's rallies in Beirut are looking for a repetition of a March 14 protest in which about one (m) million flag-waving Lebanese converged on Martyrs' Square to demand the Syrian army leave Lebanon.
The groups have continued to accuse Syria of interfering in Lebanese affairs and carrying out a campaign of bombings and assassinations in the last year that has killed other 11 people, including three prominent anti-Syrians.
Damascus has also denied involvement in these attacks.
Before the troop pullout, Syria had dominated Lebanon with its army and security services for nearly three decades, first entering in 1976 to quell a fratricidal civil war that did not end until 1990.