By some coincidence, all these architectural features (SEE ILLUSTRATION) are found at a height of almost 1.7 meters and at depths of over 2.4 meters. The coincidence can be explained firstly by the ground level chosen by the first Gothic architects, and secondly by the fact that the canons' chapter had sole use of this part of the choir (the stalls were blocked off by a screen, and several pieces of furniture prevented burials here). The same coincidence played a crucial role in enabling the site to be opened to the public beneath a concrete platform in keeping with the level of the modern-day choir.

Let’s turn to the delicate question of the clearly far-reaching date of the monument.

In the absence of stratigraphic links between the crypt and the Romanesque nave and transept (SEE ILLUSTRATION), the field of monumental archaeology has defended the synchronism of the former with the latter (dated indirectly using C14), based on their common style and construction technique. At first sight (comparative studies have yet to be completed), it can be identified as the crypt of Brussels' first collegiate church, founded in around 1047 at the behest of the Count of Louvain, Lambert II (known as Balderic), whose descendants were soon to become the Dukes of Brabant. A college of twelve canons was set up and Balderic donated the relics of St. Gudula to the church. It was then consecrated to St. Michael and St. Gudula.

In fact, the link is based almost entirely on a text which is no more than a forged charter - experts have realised this since the late 19th century - attributed to the Count of Louvain and Brussels, Lambert II. Produced by the chapter of St. Gudula, it was not written either in 1047, or shortly afterwards, but until the late 12th century. The contents nevertheless seem admissible, at least as regards the general points in question: since it refers to significant public events which were still widely remembered, it might have served to substantiate a series of far less memorable details which nonetheless involve the chapter. Some crosschecks have confirmed that the chapter was founded in around 1047 and that the relics of St. Gudula were indeed moved to the new collegiate church.

In providing permanent access to the architectural finds, there was the problem of the general stability of the cathedral choir, since the foundations of the columns were quite simply built on the floor of the crypt. The floor had to be relieved of the weight of the ballast, particularly between two opposite-facing columns which are forced to bear incredible downward loads.

Extensive reinforcement work to the substructure was approved by the "Régie des Bâtiments"
(Belgian Building Authority), with assistance from a research team, and carried out beneath the crypt floor. The marks left behind by the project - limited above ground level and restricted to less fragile archaeological remains - are barely visible today.