You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Warsaw

Context:
There are also many places commemorating the heroic history of Warsaw. Pawiak, an infamous German Gestapo prison now occupied by a Mausoleum of Memory of Martyrdom and the museum, is only the beginning of a walk in the traces of Heroic City. The Warsaw Citadel, an impressive 19th-century fortification built after the defeat of the November Uprising, was a place of martyr for the Poles. Another important monument, the statue of Little Insurgent located at the ramparts of the Old Town, commemorates the children who served as messengers and frontline troops in the Warsaw Uprising, while the impressive Warsaw Uprising Monument by Wincenty Kućma was erected in memory of the largest insurrection of World War II.

Question:
What fortification was built in the 19th century after the defeat of the November Uprising?

The Warsaw Citadel