The Castle of Populonia was born as a real fortified complex, equipped with a watchtower and defensive walls, on the hillock where in Etruscan times stood the upper town of Populonia, of which some evidence remains on the northern side of the hill.
The fortified centre was built at the beginning of the 15th century by the Appiani, Lords of Piombino, as a defensive bulwark along the northern border of the nascent state of Piombino.
Set above the entrance door to the town, it preserves the family coat of arms, with winged dragon, chivalrous helmet and allegorical ribbons, the work of the Florentine sculptor Andrea Guardi (ca. 1405 - 1476).
In order to encourage the population to move to Populonia, the Appiani provided the village with defensive walls, thus creating the Castle itself, a rather common phenomenon in the late Middle Ages.