Saarlouis (ˌzaːɐ̯luˈiː; Sarrelouis, saʁlwi; formerly Sarre-Libre and Saarlautern) is a town in Saarland, Germany, capital of the district of Saarlouis. In 2020, the town had a population of 34,409. Saarlouis, as the name implies, is located on the river Saar. It was built as a fortress in 1680 and was named after Louis XIV of France.
With the Treaties of Peace of Nijmegen in 1678/79, Lorraine fell to France. In 1680, Louis XIV of France gave orders to build a fortification (to defend the new French eastern frontier) on the banks of the river Saar which was called Sarre-Louis. Notable French military engineer, Sébastien Le Prestre de Vauban, constructed the town, which would serve as the capital of the Province de la Sarre. The plans were made by Thomas de Choisy, the town's first Gouvenour. In 1683, Louis XIV visited the fortress and granted arms. The coat of arms shows the rising sun and three Fleur-de-lis. The heraldic motto is Dissipat Atque Fovet: He (the Sun) dispels (the clouds) and heats (the earth).
In 1697, the Treaty of Ryswick made most parts of Lorraine independent again, but Saarlouis and the surrounding areas remained a French exclave. During the French Revolution, the town was renamed Sarre-Libre, but it returned to its original name in 1810. With the Treaty of Paris in 1815, Saarlouis (and the whole region later known as the Saargebiet) became Prussian.
Marshal Michel Ney, who was born in Saarlouis, was arrested and tried for treason after the failure of Napoleon I's Waterloo Campaign. Ney's attorney tried to use the Prussian annexation to save his client's life, arguing that Ney was no longer a French citizen and therefore exempt from the court's jurisdiction. Ney refused to cooperate, declaring himself to be French, and so was convicted and later executed.
After World War I, French troops occupied Saarlouis. The Saargebiet became a protectorate of the League of Nations for 15 years. In 1933, a considerable number of anti-Nazi Germans fled to the Saar, as it was the only part of Germany left outside the Third Reich's control.