Madrid is the capital and largest city of Spain. The population of the city is almost 3.2 million and that of the Madrid metropolitan area, around 6.3 million.

From the late 19th century until the Civil War, Madrid modernized and built new neighborhoods and monuments, both in the capital and in neighboring towns. In the mid-19th century the expansion of Madrid developed under the Plan Castro, resulting in the neighborhoods of Salamanca, Argüelles and Chamberí. Arturo Soria conceived the linear city and built the first few kilometers of the road that bears his name, which embodies the idea.