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Over the centuries, expanding Pau was made difficult by the city’s steep topography, formed by the confluence of the rivers Gave de Pau in the south and Hédas in the north. Carving their route in the rock, the two rivers shaped this triangular rocky spur, which is the perfect dominant position for a defensive location, but not very conducive to urban expansion. The vast spaces taken up by the royal domain, to the west and north of the spur, were also impossible to build on for a long time, and parts of them still are.
The small medieval town naturally developed to the east of the castle, in several different phases. After becoming the capital of Béarn, it was expanded then extended beyond its enclosure in the 16th century under the influence of the Albret family. From the south, it could be reached by a wooden bridge crossing the Gave, replaced by a stone bridge in 1593 at a high cost.
In the 17th century, the Counter Reformation movement, to which Louis XIII subscribed, led to several convents being set up to the east of the city, around which new suburbs gradually developed. To the north of the river Hédas, the Convent of the Cordeliers led to the construction of a bridge that crossed the ravine and linked the two shores. It was also at this time that the lower city, near the Tour de la Monnaie, became more urbanised and turned into an industrial neighbourhood.
In the 18th century, the royal road connecting Bordeaux to Spain required the construction of two new bridges in Pau, one to cross the Gave in the south and one to cross the Hédas in the north. The two routes are connected by the Place Gramont, a square built on part of the royal domain that had until then been unsuitable for building.
In 1802, a third bridge crossing the Hédas was built, which helped the city expand towards the north. This expansion became increasingly faster throughout the 20th century.