The dome, which is decorated in gold leaf and adorned with the coat of arms of the nine original provinces, casts a pleasant soft light on the gallery of portraits around the plenary meeting room.

Pages of the Constitution can be seen in two places on the ceiling. Following the declaration of independence, the text of the original Constitution was promptly drafted by the 200 members of the National Congress, the predecessor of the Parliament. It was adopted on 7 February 1831.

The Constitution describes the organisation of the new State as a constitutional parliamentary democracy and lists all the rights of the Belgians. It guarantees many freedoms, such as freedom of expression, freedom of the press, freedom of association, freedom of education and freedom of religion, amongst others. The Belgian Constitution was particularly progressive and liberal in 1831 and served as a model for the constitutions of several other countries.

The current Belgian Constitution has been significantly renewed and adapted over the years as a result, among other things, of the democratisation of the right to vote and the successive state reforms since 1970.