How many visitors to Paris could miss the Sacre Coeur, a whitewashed skeleton on the hill of Montmartre in northern Paris? At the highest point in the city, this whitewashed basilica marks the horizon on the horizon.

But why does this church look so white? Has it been painted with specialized paint? Is there an army of workers who constantly scrub it to keep it clean?

The answer is truly scientific. The church is made of travertine stone, quarried in Chateau-Landon, France. The stone releases a chemical called calcite, which means that the building remains white even when exposed to the elements.

Perhaps the architect Paul Abadie had a vision on the problems of pollution in modern cities. Whatever your reason, the use of travertine stone has stood the test of time. Travertine stone was used by the Romans two millennia earlier to build the Colosseum, the largest building in the world built primarily from this material. Subsequently, it has also been used at the Getty Center in Los Angeles.

The first stone of the Sacre Coeur was laid in 1875 and the funding for this and the remaining stones came from donations from pilgrims. The stones could be “bought”, in the form of a single brick, for example, or, more extravagantly, a whole column.

The materials are combined to include an unusual Romano-Byzantine structure with distinctive horseshoe arches. At the front, there is a divergence from the use of the characteristic white stone in the use of bronze as a material for the equestrian statues of the French national saints Louis IX and Joan of Arc.

Consecrated in 1919, the Sacre Coeur de Montmartre sends a message of Catholic purity to the city of Paris.