The Enduroman Arch to Arc Triathlon is an ultra-distance triathlon and is regarded as the “Hardest Triathlon on the planet” The triathlon starts with an 87-mile undulating run (140 km) from London's Marble Arch to Dover on the Kent coast, then a cross-Channel swim to the French coast, and finishes with a 180-mile undulating (289.7 km) bike ride from Calais to the Arc de Triomphe in Paris.