Gian Lorenzo Bernini's colonnade for St Peter's Square is a moment in which architecture designs no longer a single building but the open space between the building and the human crowd — the city. Here the 'structure' is not a volume with walls but a frame that shapes a void.

Bernini wraps the irregular area before the vast basilica in two great elliptical arms. Each arm is made of 284 giant Doric columns set in four rows; the columns are arranged so deep that the play of light and shadow shifts continuously as one walks among them, and the colonnade reads not as a solid wall but as a rhythmic, permeable forest of stone. Bernini deliberately likens these two arms to two 'embracing arms': the church symbolically opens its arms and gathers in the crowd come to the square. Architectural form turns directly into a gesture — the embrace.

The colonnade's geometry is also a visual calculation: the ellipse, unlike the circle, has two focal points; seen from the markers set at these foci, the four rows of columns align into a single row and depth seems to fold. The square is designed as a width that opens suddenly out of a narrow street — a stage dramaturgy. Bernini's colonnade is the clearest example of the Baroque turning architecture from a static object into an urban stage that takes the human in, directs, and moves them.