Alost, Or Aelst, a town of Belgium, province of East Flanders, about half way between Brussels and Ghent; pop. in 1866, 18,978. The Dender, an affluent of the Scheldt, which has been made into a canal for the accommodation of trade, passes through the town. It has considerable trade and manufactures, and was formerly the capital of Austrian Flanders. Captured by Turenne in 1667, the town was for a time in the hands of Louis XIV. It is well built and clean. In the church of St. Martin is a picture by Rubens representing " The Plague of Alost."