Leiden or Leyden, South Holland prov., W Netherlands, on the Old Rhine (Oude Rijn) River. Manufactures include medical equipment, machinery, graphic arts, and food products. The famous State Univ. of Leiden is there (founded 1575), the oldest in the Netherlands. It was a center for the study of Protestant theology, classical and oriental languages, science, and medicine in the 17th and 18th cent. The university is particularly noted for its departments of Asian studies, physics, and astronomy, as well as its botanical garden (founded 1590); the Leyden jar was invented there.