Piazza del Nettuno was given this name because it was built to give prominence to Statua del Nettuno, the statue that may be seen at its centre. In 1565 the area was totally altered and enlarged to make it suitable for the new square and the new statue. Piazza del Nettuno gave a new look to the whole area: it served as a connection with Piazza Maggiore, thus unifying an area once divided. The statue was built between 1563 and 1567 by the Flemish scupturer Jean de Boulogne, also known as “Giambologna”, and Tommaso Laureti, “Il Siciliano”.
On one side of ther square there are the municipal building, whose wall preserves the monument in honour of the partisans dead during WWII, and Sala Borsa. Along the centuries, Sala Borsa has served many purposes and in 2001 it has been adapted to host a municipal library.
On the other side of the square there is Palazzo Re Enzo. Palazzo Re Enzo was originally known as “the new palace” to distinguish it from the older Palazzo del Podestà. From 1249 it became a prison for King Enzo. King Enzo was the son of the Emperor Federico II, he was taken prisoner during the battle of Fossalta and lived in this palace until his death in 1272. At present, Palazzo Re Enzo, still known with this name, hosts exhibitions and other events.

Source: "Le Piazze di Bologna"