The Waag is a 15th-century building on Nieuwmarkt square in Amsterdam. It was originally a city gate and part of the walls of Amsterdam. Later it served as a guildhall, museum, fire station and anatomical theatre, among other things. The Waag is the oldest remaining non-religious building in Amsterdam. The building was listed as a national monument in 1970. The Waag is depicted in Rembrandt's 1632 painting The Anatomy Lesson of Dr. Nicolaes Tulp.