Arlon , Du. Aarlen, town (1991 pop. 23,422), capital of Luxembourg prov., SE Belgium, near the border with Luxembourg. Livestock and agricultural products are sold in Arlon, which is also a rail center. A small steel industry is there. A strategic point since Roman times, the town has suffered numerous attacks. Of note are Roman ruins, the Church of Saint-Donat (17th cent.), and the marketplace.