The steep staircase inside the Tower takes us to the top of the Roman structure, on which two octagonal sections rest. These were added in the extension made by military engineer Eustaquio Giannini in 1789. They rest on the existing stonework, preserving a floor where great ashlars of granite are combined in a well built lock cross welt, which might well be the original top floor of the Roman tower and where in the past the rotunda housing the beacon was built.

The restoration of the lighthouse instigated by the Consulado del Mar and under the direction of Eustaquio Giannini, in 1789, had the purpose of adapting the building to the new aids to navigation. This accounts for the substitution of the capping structure of the Tower for two octagonal sections, the second of which was designed as a beacon and modified years later.

The first section is known as the Giannini Room. An octagonal chamber with four radial pillars that leave room for a ring-shaped corridor and a continuous bench. The room is roofed by a false dome. On the upper section of one of the pillar the architect himself documented his participation in the form of an inscription that reads: “DIRIXIÓ ESTA OBRA EL THENIENTE DE NAVÍO INGO ORDINARIO DE MARINA D. EUSTAQUIO GIANNINI”. It is paradigmatic that the engineer wished to perpetuate his name in the memory of people and resorted to a solution similar to that used by architect Caio Sevio Lupo when he had commemorative inscription carved at the foot of the Tower.

Further information on Rotunda [.PDF]