Troops who have recently returned after their tour of duty in Afghanistan are marching in the historic Lord Mayor's Show in London.
David Lewis has served as Sheriff of the City of London
About 140 soldiers from the London Regiment of the Territorial Army, which returned in October, are providing the Guard of Honour.
The parade, which dates back almost 800 years, will showcase the city's culture and history.
About 6,000 people and 70 floats are taking part on the three-mile route.
An RAF flypast preceded the procession, which began at 1100 GMT from Mansion House before the march towards the Royal Courts of Justice.
There, the 680th Lord Mayor, David Lewis, will pledge allegiance to the Queen before the procession returns, via Victoria Embankment, and ends at 1400 GMT.
Mr Lewis, who is a lawyer and a businessman, served as Sheriff of the city in 2006-2007.
The parade covers a three-mile route
The last fully operational World War I tank, Mk V , which has been housed at the Tank Museum in Bovington, Dorset, will also be a special feature in this year's parade.
King's Troop Royal Horse Artillery and the Household Cavalry Mounted Regiment will accompany the soldiers in the march.
The event ends with a fireworks display from a barge in the Thames moored between Blackfriars and Waterloo bridges.
At least 40,000 people were expected to line the streets to watch the event.
The roads in the area will remain closed until 1400 GMT.
Roads that will be shut are Gresham Street, Princes Street, Bank, Mansion House, Poultry, Cheapside, New Change, St Paul's Church Yard, Ludgate Hill, Fleet Street, Strand, Aldwych, Victoria Embankment, Queen Victoria Street and Bank.