This curious object is a spur and is attached by the leather strap to the heel of a riding boot. It consists of a metal U shaped yoke with a protruding wheel of spikes that rotates. This is called a rowel.  Spurs are worn in pairs - one for each foot - and are used by equestrians to help control and direct a horse. 

Spurs have been used for centuries, particularly in the military; spurs made from iron or bronze were worn by the ancient Celts, Romans and Greeks.  The word comes from an old Anglo-Saxon spura. Medieval knights wore silver coated spurs and the phrase “to win his spurs” meant to gain his knighthood. You might also have noticed cowboys wearing spurs in films. Spurs are worn with the leather strap over the front of the ankle and the metal U cupping the back of the heel. The rowel sticks out behind the heel so that the rider can use it to touch the ribs of the horse. When used carefully, spurs are a subtle way of controlling a horse although a rider has to be very experienced so as not to hurt or frighten the horse.  

These spurs date from the First World War when horses were heavily used in battle and for transport.  Perhaps you have read War Horse by Michael Morpurgo? This novel tells of the experiences and adventures of Joey, a horse sold to the cavalry and sent to the front in France.  One of the last cavalry charges was at the Battle of the Somme in 1916. 432,000 British soldiers were killed or wounded in the battle of the Somme. The French lost nearly 200,000 men and the Germans lost an estimated 500,000. More than 100,000 horses died. With trench warfare, the use of cavalry diminished.

On the city streets today you may see horses used in funerals. Police sometimes use them in their daily patrols, and to control riots.