Main Square, Porticoed square in Sol, Spain.

Plaza Mayor is a rectangular porticoed square in Sol, Madrid, measuring 120.9 by 93.06 metres, enclosed by three-story residential buildings with 237 balconies facing the square. Ten entrances, six through large arches, open to surrounding streets, and a bronze equestrian statue of Philip III stands on a stone pedestal in the centre.

The site began as the Plaza del Arrabal, a marketplace outside the medieval walls. Philip II commissioned Juan de Herrera to redesign it in 1560, and Juan Gómez de Mora completed the enclosed square in 1619 under Philip III. After fires in 1631, 1670 and 1790, Juan de Villanueva reduced the buildings from five to three stories and added the corner arches.

The arcade arches carry names like Arco de Cuchilleros or Arco de la Sal, recalling old craft quarters and goods once traded here. On Sundays, stamp and coin collectors gather beneath the porticos to exchange or offer their finds.

The square is closed to road traffic, with ten entrances and nine gates giving access; the Arco de Cuchilleros, at the southwest corner, has a tall arch because of the drop to the Cava de San Miguel. The Sunday stamp and coin market runs in the morning under the arcades. The 237 balconies face inward, so the paving is the only open ground.

The facade paintings on Casa de la Panadería date from 1992, when artist Carlos Franco created mythological scenes tied to Madrid folklore. Beneath the plaza paving runs an underground passage that once linked royal chambers and remains sealed today.