The Inspection of the Line

Her Majesty The Queen and The Duke of Edinburgh, drive down The Mall in Queen Victoria's 1842 ivory-mounted phaeton drawn by a pair of matched Windsor Grey horses, so named from Victorian times when grey horses were used for drawing private carriages at Windsor. The Postillion is dressed in full State Postillion Livery.
The Queen's ceremonial horses are kept at the Royal Mews, where there are currently about 30 horses. The carriage horses draw The Queen's carriages and coaches in State processions and on ceremonial occasions throughout the year. Many of the carriage horses, in addition to their ceremonial duties, have represented Great Britain in national and international carriage driving competitions (in which The Duke of Edinburgh has competed since 1973).
The Queen last rode a horse on a ceremonial occasion at Trooping the Colour in 1986; the horse was a black mare named Burmese, given to The Queen by the Royal Canadian Mounted Police, which The Queen rode for Trooping the Colour from 1969 until the mare's retirement in 1986.
The Sovereign's Escort, consisting of the mounted troops of the Household Cavalry Mounted Regiment and the Mounted Bands, accompany Her Majesty.
The crowd stand in respect as the Queen crosses the parade ground.

The Royal Colonels, who are mounted following the Queen, salute the colour as they pass. The Queen arrives at the dais at exactly 11 o'clock. The Guards present arms whilst the Massed Bands play the National Anthem.
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There now follows the 'Inspection of the Line' whilst the Massed Bands of the Household Division play patriotic airs from around Britain. The Queen remounts the Phaeton, followed by the mounted Royal Colonels: HRH The Princess Royal, Gold Stick in Waiting and Colonel of the Blues and Royals; HRH The Duke of Kent, Colonel of the Scots Guards; HRH Prince Philip, Colonel of the Grenadier Guards and HRH The Prince of Wales, Colonel of the Welsh Guards.

In procession with Her Majesty are also the Master of the Horse, The Crown Equerry, The Equerries in Waiting and The General Officer Commanding London District. The carriage turns before No. 6 Guard to the left of the line. The coachman acknowledges the Colour and the Royal Colonels salute.

Now, The Royal Colonels pass behind No. 6 Guard as Her Majesty makes her way towards the massed mounted bands, the Sovereigns Escort of the Household Cavalry and the Kings Troop, Royal Horse Artillery.
The Queen arrives back at the dais and takes her place for the rest of the ceremony.