Madrid is composed of 21 districts, each broken down into several neighborhoods. The most central district is called just that, Centro. Within this district you'll find all of Madrid's oldest neighborhoods: Palacio, Sol, La Latina, Lavapiés, Barrio de las Letras, Malasaña, and Chueca. Other well-known districts, which we'll call neighborhoods for the sake of convenience, are Salamanca, Retiro, Chamberí (north of Centro), Moncloa (east of Chamberí), and Chamartín.
The city of Madrid dates back to the 9th century, but its perimeter wasn't enlarged by much until the mid-19th century, when an urban planner knocked down the wall built in 1625 and penciled new neighborhoods in what were formerly the outskirts. This means that even though there are now more than 3.3 million people living in a sprawling metropolitan area, the almond-shaped historic center is a concentrated area that can pleasantly be covered on foot.