For nearly 700 years, the Palace of Coudenberg was the seat of government which, form the 11th century until its destruction in 1731, ruled over the Duchy of Brabant (the area that is now the southern Netherlands and northern Belgium). Following a careless moment in 1731 (one which was covered up for quite some time for fear of embarrassing the royalty) the whole thing burned to the ground.
As recently as 1998, the remains of the ancient palace were unearthed under the current Place Royale and have been extensively excavated and preserved. These ruins can be visited via the BELvue Museum
Metro Stop: Parc