On a grassy lawn wedged into the northwest corner of the city walls, medieval Pisans created one of the most beautiful squares in the world. Historically dubbed the Campo dei Miracoli (Field of Miracles) , Piazza del Duomo contains an array of elegant buildings that heralded the Pisan Romanesque style.

But Piazza del Duomo isn’t the central plaza in town as in most Tuscan cities. When it was built between the 11th and 13th centuries, the square was against the city walls, surrounded by farmland. But this peripheral location also somehow plays a role in the piazza’s uniqueness. A very large but hidden part of its appeal, aside from the beauty of
the buildings, is its spatial geometry. The piazza’s medieval engineers knew what they were doing. If you take an aerial photo of the square and draw connect-the-dot lines between the centers, doors, and other focal points of the buildings and the spots where streets enter the piazza, you’ll come up with all sorts of perfect triangles, tangential lines of mathematical grace, and other unfathomable hypotenuses.

Incidentally, only the tourist industry calls it Campo dei Miracoli. Pisans think that’s just a bit too much and refer to it, as they always have, as Piazza del Duomo...

Italy’s biggest baptistery (104m/341 ft. in circumference) was begun in 1153 by Diotisalvi, who gave it its lower Romanesque drum. Nicola and Giovanni Pisano “Gothicized” the upper part from 1277 to 1297 and Cellino di Nese capped it with a Gothic dome in the 1300s. Most of the exterior statues and decorative elements by Giovanni Pisano are now kept in the Museo dell’Opera del Duomo (see below), and only a few have been replaced here with casts. It may not look it, but if you include the statue on top, this building is actually taller than the Leaning Tower across the square...

The other main attraction of the baptistery is its renowned acoustics.

It is citation from "Frommer’s Florence, Tuscany & Umbria" travel guide by John Moretti, 7th Edition, 2010, (page 288)