1690: Seyne is in danger: the Duke of Savoy has just joined the league of Augsburg.
At this time, the building of the fort is not on the agenda. On the other hand, the medieval precincts were no longer suitable for the defense of the city, and the military engineer Niquet received from Vauban the necessary instructions to draw up plans for the new enclosure. Niquet produced the plans and made the route (fig.1).

The enclosure will be supported by 9 towers, 3 of which are protruding on the enclosure and whose walls are pierced with loopholes. They are merely simple one-storey buildings, not vaulted, covered with a framework, rectangular with an edge. It is penetrated by a "throat". The "Butte Tower" will become the powder store.
The work began in 1691 but Niquet was caught by an invasion of the Marquis de Parelles (general Savoyard). From this event, the necessity of the citadel is essential.
In 1692, Richerand, Regional Director of Fortifications, takes over from Niquet and draws up plans for the citadel

On this plan we see that the "Tower of the Butte" is integrated into the citadel, as well as the Great Tower.
On inspection tour in 1700, Vauban strongly criticizes what he discovers in Seyne and works on the improvements to be made. He draws up a complete plan and gives his instructions. The tower of the butte will be transformed into a powder magazine:
"Put the whole lower floor into a very dry cellar for the purpose of putting the munitions of war and of mouth on it, and to make one for a powder magazine and wicks, balls, gun-stones, grenades, and sacks"; Drill vents at the bottom of the walls so that the air can circulate at best.

The first floor, "pretty enough" will be the place of arms.