The Millau Viaduct has seven piers that support its horizontal deck. They are numbered from 1 to 7, from north to south of the viaduct, and pier P2 holds the world record for height with 800 ft (245 m). Their height varies according to the topography of the site on which the viaduct extends as well as to its length profile. The shape and dimensions of each pier have been designed to resist the vertical load imposed by the deck, the head displacements due to the thermal expansion of the deck, and the effect of the wind. The piers are all monolithic at their base and then split on their upper part in order to cope with different constraints.