In spite of protests from the Count of Provence and the population of Avignon, Philippe-le-Bel pressed ahead and built a gatehouse at the end of the bridge.

The tower and gatehouse formed part of a fortress with a curtain wall that enclosed several buildings including a chapel and a residence for the châtelain.

The treaty of Meaux-Paris, signed in 1229 at the end of the Albigensian Crusade, handed the French crown land on the right bank of the Rhône from Pont-Saint-Esprit to the Mediterranean and a joint interest in the city of Avignon.

[1][2] As a consequence Philip gave up his share of the strategic Saint-Bénézet Bridge across the Rhone which had been built between 1177 and 1185 by the city of Avignon.

The abbey had been founded at the end of the 10th century and possessed extensive property with over 200 churches spread over a wide area of southern France.

[4] In 1290 Philip IV instructed Adam de Montcéliard, the sénéchal of Beaucaire, to negotiate an agreement with the abbey to cooperate in the defense of the right bank of the Rhone.

[1][5] It meant that the abbey surrendered temporal power but obtained protection from the unwanted pressure from the city of Avignon which wished to control both banks of the Rhône.

This initial construction work almost certainly included the building of a curtain-wall, a well, a bread oven, a kitchen and some form of lodging for the châtelain and the guards.

[9] Charles II, Count of Provence objected to the position of the new fortress and wrote letters protesting that the foundations of the tower were right next to the bridge which was built on his property.

Around 1350, during the reign of either Philip VI or his successor John II, an additional storey was added to the tower with a rectangular turret on the top.

[13][14] During the period of the Avignon Papacy the fortress saw much activity with high ranking church officials, princes and notables crossing the bridge.

Eighteenth century drawings show that access to both the fortress and the harbour was controlled by gates on the path leading up from the river bank along what is now the Montée de la Tour.

Probably, as a result, in 1787, Quintin de Beuverd, captain of the Corps Royal du Génie, produced a detailed report on the state of the buildings.

These events were overtaken by the French Revolution in 1789 but the surviving documents allow historians to study the layout of the fortress.

[20] In 1834 part of the limestone rock around tower was cut away to create a new access route to the port on the Rhône.

The construction of roads and a car-park have obliterated almost all traces of the surrounding buildings, but fortunately, the many documents and pictures that survive in the archives can be used to study the details of the original structure.

[26] The floors are connected by a well-conserved narrow spiral staircase only 1 m (3 ft 3 in) in width located in the northwest corner of the building.

[27] Areas of protruding stonework on the north and east sides the tower appear to be the remains of the bonding of a defensive curtain wall.

The third crest, which has what appears to be an oblique row of three roses, is probably that of Pope Clement VI who purchased the town of Avignon from Joanna I of Naples in 1348.

In two of the arched niches, and also barely visible on the west wall, there is an interlocking hexagonal pattern in red ochre lines that is decorated with foliage curling around a large rose with five petals.

The rib vaulting is divided into two bays as on the ground floor but the six corbels and the ceiling bosses are decorated with finely carved busts or foliage.

The entrance was perhaps originally served by a wooden staircase but when the gatehouse was constructed it gave direct access to the châtelain's residence.

The position is surprising as it would have been almost above the quarters of the châtelain and it is possible that the structure was originally a bartizan which was converted into a garderobe when the upper floors were used as a prison.