The Medici Fortress of Piombino was designed by Giovanni Camerini and constructed between 1552 and 1557 for Cosimo I de’ Medici. It has an elongated star-shaped design with bastions at the corners, typical of the fortifications of the 15th century; a similar construction can be found across the water in Portoferraio on the island of Elba. An older castle with a centralized ground plan dating to the second half of the 15th century originally stood on the site, but was incorporated into the new fortress. During his sojourn in Piombino in 1504 Leonardo da Vinci studied its architecture, which inspired him to design his own circular tower, as can be seen in the Codex Madrid II.
The fortress complex served both as an observation post and a bulwark to defend the town from attack by sea or from the coast. It was important for Piombino to defend its position, which was vital to its commercial activities, in particular the transport of goods and iron ore between the mainland and the island of Elba. This activity dwindled when in the middle of the 19th century the castle was commandeered for use as a state prison. The building was completely renovated for this purpose, and served as a penal institution until the middle of the 20th century. It has since been restored and opened to the public, who can now see what it must have looked like during the past periods in its history.
Another portion of the town’s defences have been restored and now house the Museo del Castello e della Città, where permanent and temporary exhibitions can be seen. A collection of ancient artefacts including ceramics and metal objects allow the visitor to study the most important chapters in the history of the castle and the surrounding territory.