The site, exten­sive­ly for­ti­fied from the 17th to 19th cen­turies, rep­re­sents the largest bul­warked dry-ditch sys­tem in the world. With­in its walls, the town con­tains bar­racks and oth­er mil­i­tary build­ings as well as church­es and monas­ter­ies. While Elvas con­tains remains dat­ing back to the 10th cen­tu­ry ad, its for­ti­fi­ca­tion began when Por­tu­gal regained inde­pen­dence in 1640. The for­ti­fi­ca­tions designed by Dutch Jesuit padre Cos­man­der rep­re­sent the best sur­viv­ing exam­ple of the Dutch school of for­ti­fi­ca­tions any­where. The site also con­tains the Amor­eira aque­duct, built to enable the strong­hold to with­stand lengthy sieges.