The Castle of Cabra was raised, within the walled enclosure in the North West of the present town, on a spot high enough to overlook the whole town. It is said that it had a central square surrounded by a strong wall with eighteen towers where eight or ten thousand men could march. At present, most of what remains, it is enclosed within the constructions of the present School of the Escolapias. Among the constructions we have been able to locate the wall, of which something more than half still remains and to track the rest until we were able to determine, quite accurately, the plant of the enclosure which must have been quadrangular, of about 76x47m. The thickness of the walls is about two meters and sixty centimetres, approximately. The fact that the rest of the walls- and possibly of towers are surrounded by modern constructions hinders their thorough study.
As far as the towers are concerned, we can say that two of them are well known, plus the location of other two, that were to the sides of the present front door to the enclosure. In the centre of the East wall and half way out is the tower of Homage. It is almost square shaped and it is more than twenty meters high. At about eleven meter above ground level there is a squared chamber with an eight sided vault ceiling with tubes in the angles. The other tower is located in the northwest angle. It is of squared plant, with the angle that looks to the interior of the chamfered enclosure. The lower part is massive and in the upper part there is a chamber with a barrel vault. It still keeps about ten meters of its height and its maximum surface on the plant is 6.5×6.3m.
Of the other two acknowledged towers there only remain their foundations upon which modern constructions have risen.
References:The historical centre of Briançon is a strongly fortified town, built by Vauban to defend the region from Austrians in the 17th century. Its streets are very steep and narrow, though picturesque. Briançon lies at the foot of the descent from the Col de Montgenèvre, giving access to Turin, so a great number of other fortifications have been constructed on the surrounding heights, especially towards the east.
The Savoyards made two raids into French territory in 1691 and 1692. As a result, Vauban was dispatched to inspect the frontier defences, which had been ill-equiped to deal with the attack from Savoy. He returned to the area in 1700 to check on the progress that had been made since his first visit. When Vauban visited Briançon, work on the defences had already started under a local engineer, Monsieur d"Angrogne in 1692.