Marble is made of calcium carbonate, CaCO3, which is also what limestone is made from. The only difference between limestone and marble is the crystalline structure. Limestone crystals are much smaller than that of marble, and limestone is much more porous.
Marble and limestone are common building materials due to their durability. However, since the onset of acid rain, these materials are at risk from erosion. Acid rain contains sulfuric acid, which reacts with calcium carbonate to create aqueous ions. It happens on the surface of the marble or limestone and the fine details on the facade of the structures made with them, are being lost.