Tortosa (tōrtō`sə), city (1990 pop. 29,970), Tarragona prov., NE Spain, in Catalonia, on the Ebro (Ebre) River. It has a fishing industry and light manufacturing, producing cement, clothing, and pharmaceuticals. Agricultural products are traded. A Roman colony (then known as Dertosa), the town later fell (8th cent.) to the Moors, who held it against repeated Christian onslaughts until its conquest (1148) by Raymond Berenger IV. There is a seismological observatory nearby.