Its mission was to control and watch the area against possible pirates or French invasion expeditions. Its defense was vital for the communitacion system that used smoke signals during the day and fire at night, and that could be seen from El Toro Mountain or from a second Tower in the harbour of Fornells.

Archaeology at Sanitja Harbour. The vital need for defense from the outside, the prevention of an enemy, has marked Sanitja throughout its history. Minorca’s strategical place, both for vigilance and as a refuge and stop in the maritime routes, has left in this place a rich archaeological treasure.

A military camp, a Roman city and a Muslim mosque are human settlements that since Roman times testify of Sanitja’s long occupation.

Sanitja was the place chosen by the Roman general Quintus Caecilius Metellus, in 123 B.C., to set up a soldiers garrison that would take the Balearics, and in this way he procured for himself fame and glory in Rome, and the nickname of "Balearicus".

At the end of the 1st century A.D., army veterans decided to set their residence in Sanitja, and some inhabitants from the Talayotic settlements closer to the coast, must have built the first houses in the most comfortable area of the bay. In that place the Roman city of Sanisera was built.

The city lasted six hundred years, and today waits asleep to become a Princess that will accompany the Lighthouse King, in a time when archaeologists rescue her from her oblivion.