The oldest building in Antwerp is an 800-year old castle known as 'The Steen' (stone in English).

Only
one building of the old part of Antwerp escaped demolition
when the quays on the river Scheldt were constructed
in the 19th century: 't Steen (the Stone). The Steen
was built around the year 1200 as the fortification
of the alluvial mound. It was named Steen, which is
Dutch for stone, as it was one of the first buildings
constructed in stone.
The Steen was altered several times during history.
It was extended during Charles V's reign around 1520
by the architects Keldermans and De Waghemakere. The
chapel above the entrance dates from this period.
From 1549 till 1823 the building served as a prison
and in 1862 it became an archeological museum. The Steen
was renovated again in 1890 and a wing in neo-gothic
style was added.
Today the Steen houses the National Maritime Museum.
Adjacent to the ancient structure, the Maritime museum
also displays several old vessels in open-air.