A bastion in the old city fortifications, around 1600 San Giorgio was guarded by six unarmed German soldiers and in the early 18th century  was used as a powder store.

In 1819, when Liguria was annexed to Piedmont, the bastion was expropriated and returned to the Fortification Service, in order for it to build a fortress. The owner of the house and garden inside the bastion was paid 13,350 liras.
In 1849, fearing that the Savoy might let Austria rule their city, the people of Genoa rose up in protest and occupied the Fortress of San Giorgio.
In the following drawing, dated 1852, the fortress appears as in ruins.

The project for a reconstruction of the fortress as an Astronomical Observatory dates back to 1858, for time keeping and time preserving purposes.
The Fortress of San Giorgio has been home to the Italian Hydrographic Office since 1872.