The Quack monument or Marie-Adolffontein is a monument in Nijmegen, in the Dutch province of Gelderland.
The Quack monument was originally founded in 1926 from a legacy of Arnoldus Burchard Adolphus Quack. Quack was alderman of the municipality of Nijmegen from 1902 to 1919. The monument is named after him and his twin sister Maria Christina. Quack left his legacy to the municipality of Nijmegen under the condition that a fountain, the Marie Adolphron named after his sister, would be erected.
Architect Willem Bijlard designed the monument that contains four fountains and four bells at the base and four lanterns at the top. The lower part is made of granito. The obelisk is made of red granite with carved art-deco ornaments.
Coordinates 51°50'38.19" N 5°51'28.565" E