The castle is set upon unusual foundations, laid in the shape of a polygon, and is surrounded by powerful walls which follow the shape of the buttress on which they are built, and which is dominated by a ballast pentagonal tower. The castle is situated on a hillock that was claimed by Genova in 1152, an event that provoked the Pisans to conquer the seaside town.
The architectural structure of the castle was influenced by a variety of styles, each one corresponding to that of a different area of Lerici. In the first half of the 13th century, the Pisans added a large rectangular hall, and a chapel dedicated to Santa Anastasia, to the pre-existing main tower. It was later reclaimed by Geneva in 1256, who further reinforced the tower with the building of protective walls around the north-eastern part of the courtyard, and finished off the construction of the castrensian chapel. In 1555, powerful walls were erected over the sheer drop to the sea, transforming the castle into the imposing structure it is today. The castle currently hosts the Museum of Palaeontology and has also carefully maintained the chapel of Santa Anna, which is built in the ligurian gothic style and is engraved with an inscription documenting the Genevan reclamation of Lerici.