The Casa Battlló is the most celebrated building on the "Block of Discord" in Barcelona's Eixample district. It stands at Passeig de Gracia and is one of the best-known works of Antoni Gaudi.

The house was originally built between 1875 and 1877. In 1900 it was bought by the rich industrialist Josep Battló i Casanovas who commissioned Gaudí to tear down the old house and reconstruct a new one. Gaudí however convinced Battló to remodel the existing building. Between 1904 and 1906 Gaudí redesigned the facade and roof, added an extra floor and completely remodeled the interior.
The facade is a perfect example of Gaudi's Genius. It is made of sandstone covered with colorful trencadis (a Catalan type of mosaic). Typical of Gaudí, straight lines are avoided whenever possible.
Balconies at the lower floors have bone-like pillars, those on the upper floors look like pieces of skulls.
These features gave the house the nickname 'House of Bones'. The enlarged windows on the first floor gave it another nickname, 'House of Yawns'.
The colorful scaled roof recalls a reptile skin. According to some authorities on Gaudí architecture, the roof represents a dragon; the small turret with a cross would symbolize the sword of St. George stuck into the dragon.
The bones and skulls on the facade represent all the dragon's victims.
In 2004 the Casa Battlló received the Prix Europa Nostra to the Cultural Heritage and in July 2005 it was declared a World Heritage Site by the UNESCO.