Casa Milà, popularly known as La Pedrera or "The stone quarry", a reference to its unconventional rough-hewn appearance, is a Modernista building in Barcelona, Catalonia, Spain. It was the last private residence designed by architect Antoni Gaudí and was built between 1906 and 1912.

Casa Milà is characterized by its self-supporting stone facade, meaning that it is free of load-bearing walls. The facade connects to the internal structure of each floor by means of curved iron beams surrounding the perimeter of each floor. This construction system allows, on one hand, large openings in the facade which give light to the homes, and on the other, free structuring of the different levels, so that internal walls can be added and demolished without affecting the stability of the building. This allows the owners to change their minds at will and to modify, without problems, the interior layout of the homes.

The facade is composed of large blocks of limestone from the Garraf Massif on the first floor and from the Villefranche quarry for the higher levels. The blocks were cut to follow the plot of the projection of the model, then raised to their location and adjusted to align in a continuous curve to the pieces around them.

Viewed from the outside the building has three parts: the main body of the six-storey blocks with winding stone floors, two floors set a block back with a different curve, similar to waves, a smoother texture and whiter color, and with small holes that look like embrasures, and finally the body of the roof.

The building uses a completely original solution to solve the issue of a lobby being too closed and dark. Its open and airy courtyards provide a place of transit and are directly visible to those accessing the building. There are two patios on the side of the Passeig de Gracia and of the street Provence.

Patios, structurally, are key as supporting loads of interior facades. The floor of the courtyard is supported by pillars of cast iron. In the courtyard, there are traditional elliptical beams and girders but Gaudí applied an ingenious solution of using two concentric cylindrical beams with stretched radial beams, like the spokes of a bicycle. They form a point outside of the beam to two points above and below, making the function of the central girder a keystone and working in tension and compression simultaneously. This supported structure is twelve feet in diameter and is considered "the soul of the building" with a clear resemblance to Gothic crypts.

According to Wikipedia