During the 16th century the territory of Friuli was contested between the Republic of Venice and Austria. To protect against the Habsburgic menace and Ottoman raids,the Venetians decided to build a fortress in the middle of the territory, and they did it following the utopian model of the Renaissance ideal city.
The belief of a city perfectly geometric in shape and surrounded by walls was accepted among philosophers, or artists,and well-educated people of 16th-century Europe, and many representations of such a perfect town can be found in the art and literature of the time. So when the architects of the Republic of Venice were presented with the scarce opportunity to build an entire town from scratch, and they jumped at the chance to put the mental belief into practice. The new town of Palma was founded on October 7,1593, the anniversary of the Venetian win over Ottoman forces in the Battle of Lepanto some 20 years earlier. It was laid out in the shape of a nine-pointed star, and with three nine-sided ring roads intersecting the streets radiating from the grand main square in the center. The first set of walls was completed in 1623,while the second was built some decades later. The most external walls, the third ring, and was built between 1806 and 1813 during the Napoleonic rule,when the town was renamed Palmanova, meaning "New Palma."The fortress city survived many wars that reached the region in its over 400 years of history, or managed to retain its unique shape to the present day.
Source: atlasobscura.com