Roman and medieval times

Before the Roman conquests of Gaul, the territory of Arlon and a vast area to the southeast were settled by the Treveri, a Celtic tribe. The local population adapted relatively easily to Roman culture. The number and quality of sculpted stones and monuments that have been unearthed in the area demonstrate that the vicus of Orolaunum quickly became a commercial and administrative centre of Roman civilization. The Germanic invasions of the 3rd century destroyed most of these early advances, despite the defensive walls that had been built on the Knipchen hill to protect the vicus.

During most of the Middle Ages, the population still used the earlier buildings such as the thermae. In 1060, Waleran I of Limburg, Count of Arlon, built a castle on the Knipchen hill in the centre of the town.

A dynasty of counts of Arlon began with Waleran I, Duke of Limburg. On the death of Duke Waleran III in 1226, Arlon passed to his son from the second marriage, Henry V the Fair, Count of Luxembourg, and became part of the county of Luxembourg. Thus, in the Tournament of Chauvency, his son Henry the Lion bore the title of Marquis of Arlon.

In the 13th century, the only women's Cistercian abbey known to date was built in Clairefontaine.

15th century until the French Revolution

The Duchy of Luxembourg itself, of which Arlon was dependent, became part of the Burgundian Netherlands under Philip the Good in 1441. After Charles V's abdication of his empire to his son Philip II of Spain in 1556, a troubled period started for the whole region with continuous wars involving France, Spain and the Southern Netherlands. In 1558, nearly half of the city, including its castle, was destroyed by the French troops of Francis, Duke of Guise. In the 17th century, Capuchin friars built a convent on the ruins of the castle and the French strengthened the defensive walls according to Vauban's designs. An accidental fire destroyed a large part of the city again in 1785.

Modern times

On 9 June 1793 the French Revolutionary troops opposed the Austrians just outside Arlon. The French emerged victorious and took over the city from Austrian rule. They expelled the Capuchin friars and used their convent as a hospital.

In June 1815, after the defeat of Napoleon in the Battle of Waterloo, Arlon went back to government of the Grand Duchy. By the Treaty of London in 1839, the grand duchy became fully sovereign and in turn geographically larger western part of the duchy, i.e. the province de Luxembourg including Arlon city was given to newly created Kingdom of Belgium.

Arlon was one of the first victims of the German invasion in 1914 as 121 inhabitants were executed on 26 August, on the orders of Colonel Richard Karl von Tessmar.

Its territory was again among the first to be invaded at the onset of World War II. Allies moved into Belgium on 10 May 1940 and Arlon was defended by French troops, but they were not able to stop the German invasion.

Twin towns — sister cities

Arlon is twinned with:

• Saint-Dié-des-Vosges, France since 1962
• Diekirch, Luxemburg
• Bitburg, Rhineland-Palatinate, Germany since 1965
• Sulphur, Louisiana, United States
• Hayange, France
• Alba, Italy since 1 March 2004
• Market Drayton, England, UK