The Lord Mayor's Show is the largest unrehearsed procession in the world. Three and a half miles of people, horses, vehicles, soldiers, bands, bicycles and giant fish have to be assembled early in the morning, marched to Aldwych, hidden away, lunched, reassembled in the right order, marched back to the City and eventually dispersed.

Meanwhile the streets have been inspected, the construction works approved, the manhole covers lifted and sealed again, the marshals and police briefed, the participants organised and the coach brought very carefully round to the Guildhall. The new Lord Mayor has been rehearsed, television cameras arranged, finances held together and the roads of the City covered in sand for the comfort of the horses.

People are often surprised to see that the timetable for the Show is calculated to the second. The procession would be impossible without that kind of accuracy. A delay of a few seconds opens a gap ahead and causes more delays behind. Gaps and delays are not allowed.

The person who prepares all this and makes it work on the day is Dominic Reid: architect, soldier and Pageantmaster of the Lord Mayor's Show.

When you see the Pageantmaster he will either be on a horse or standing in the back of a ceremonial Land Rover wearing a remarkable hat. He will look calm and perhaps a bit relieved, giving no sign that he was up at 4am inspecting the route or that he has worked for nine months to make the Show look as though it requires no effort at all.