1978 Prix de l'Arc de Triomphe

The 1978 Prix de l'Arc de Triomphe was a horse race held at Longchamp on Sunday 1 October 1978. It was the 57th running of the Prix de l'Arc de Triomphe.

The winner was Alleged, a four-year-old colt trained in Ireland by Vincent O'Brien and ridden by Lester Piggott. Alleged, the 14/10 favourite, defeated the mare Trillion by two lengths, with Dancing Maid a further two lengths back in third. Alleged became the sixth horse to win the race twice after Ksar, Motrico, Corrida, Tantieme and Ribot. The winning time was 2:36.1.

Race details

 * Sponsor: none
 * Purse:
 * Going: Dead
 * Distance: 2,400 metres
 * Number of runners: 18
 * Winner's time: 2:36.1

Full result
* Abbreviations: ns = nose; shd = short-head; hd = head; snk = short neck; nk = neck

Winner's details
Further details of the winner, Alleged.
 * Sex: Colt
 * Foaled: 4 May 1974
 * Country: United States
 * Sire: Hoist The Flag; Dam: Princess Pout (Prince John)
 * Owner: Robert Sangster
 * Breeder: June McKnight