The Waag ("weigh house") is a 15th-century building on Nieuwmarkt square in Amsterdam. It was originally a city gate and part of the walls of Amsterdam. The building has also served as a guildhall, museum, fire station and anatomical theatre, among others. The Waag is the oldest remaining non-religious building in Amsterdam.  The building has held rijksmonument status since 1970.  The Waag is depicted in Rembrandt's 1632 painting The Anatomy Lesson of Dr. Nicolaes Tulp. The surgeons' guild commissioned this painting for their guildhall in the Waag.