Spa is a Belgian town located in Liège Province, and the town where the term spa originates. Spa is one of Belgium's most popular tourist destinations, being renowned for its natural mineral springs and production of 'Spa' mineral water, which is exported worldwide. In 2021, the town became part of the transnational UNESCO World Heritage Site under the name 'Great Spas of Europe'.
As the site of cold springs with alleged healing properties, Spa has been frequented as a watering-place since the 14th century. It is the town of Spa which has become eponymous with any place having a natural water source that is believed to possess special health-giving properties, known as a spa. The Spa town grew at that time, in the oldest iron and steel centre of Liège Province. The ban Spa was created around 1335 and included two urban concentrations, vilhe of Creppe and vilhe Spas, 2 kilometres away. Prior to the exploitation of mineral water, the steel industry developed communication lines, which made it possible to develop the spa town.
Kristiansten Fortress was built to protect the city against attack from the east. Construction was finished in 1685. General Johan Caspar von Cicignon, who was chief inspector of kuks fortifications, was responsible for the new town plan of Trondheim after the great fire of 18 April 1681. He also made the plans for the construction of Kristiansten Fortress.
The fortress was built during the period from 1682 to 1684 and strengthened to a complete defence fortification in 1691 by building an advanced post Kristiandsands bastion in the east and in 1695 with the now vanished Møllenberg skanse by the river Nidelven. These fortifications were encircled by a continuous palisade and thereby connected to the fortified city. In 1750 the fortress was modernized with new bastions and casemates to protect against mortar artillery.