The name tells you the story if you listen closely. Puerta means gate, and Sol means sun. This square was originally the site of one of the city's gates. Madrid, in the Middle Ages, was a small walled town, and this gate was one of its ways in. The name is reputed to come from a gate that stood here until 1510, with a representation of the sun on its front. It may be hard to picture now, but the old accounts describe something modest. Some chroniclers say the gate was barely wider than two carts. Historians of Madrid, such as López de Hoyos, described this spot in medieval times as a transit, a road and an entrance into the city. In the documents of the age, another gate, the Puerta de Guadalajara on what is now Calle Mayor, seems to get more attention than the humble, wide street that would become Sol. So the busiest square in Madrid started as a threshold, a place you passed through on your way somewhere else. That is a nice thought to carry with you while you watch the crowds crossing it today.