Bernini - St Peters Square (1656)
Tourists visit St Peter's Square rather with a touristical guide than with a measuring tape with a lenght of more than 200 m to control wheater the square is elliptal or not.
Looking to the plan, you can easily see that Bernini desigens St Peters Square as an ovaal according to the well known scheme of Serlio based on equilateral triangles.
You can notice that the boundaries of the colonnade match with the boudaries of the circular arcs if the smallest size, to which a finishing construction is added.
centro del colonnato
The centers of the two red circular arcs of the oval are marked on the square by a stone bearing the inscription centro del colonnato. Indeed they are what they are: centers of circles.
In contrast the foci of the ellipse that approximately matches the oval roughly correspond with the fountains on the square
