Puerta del Sol (Sun Gate) is the most popular and commercial area in the old town. Five hundred years ago it was just another city gate with an image of the sun drawn on it, hence its name. Nowadays, the square is famous for being the center of the national road network. The plaque on the pavement outside the old Post Office building denotes 'kilometer 0'. The distance between Madrid and every other part of Spain is measured from here. Thousands of locals and tourists flock to the square once a year to await the chimes of the clock that officially announces the New Year.