The first collegiate church and its frontispiece were pulled down to make way for the Gothic church,
which was built gradually between 1225, and the 15th century. In theory the ongoing demolition project was restricted only to those parts which exceeded the level chosen by the Gothic architects. Would it not
be possible, during excavation work on the new foundations of the modern-day cathedral, to locate all those architectural features which had not hindered the rebuilding project? Not to mention the endless digging and excavating caused by almost a half millennium of burials (that is, until Emperor Josef II's 1784 edict banning interments within the city). The remains of the ancient walls would have mostly been destroyed.

Despite this, excavation work made it possible to entirely reconstruct the plans, owing in part to the symmetries observed by the Romanesque builders. The transcription was in fact discovered in situ in the new floor of the Gothic nave. Included here is a range of excellent architectural evidence which attentive visitors can observe in special mesh-covered shafts. Most of them are to be found in the north aisle.
From west to east:
- demolition of the old west facade to attach the frontispiece;
- the base of one of the pillars from the nave, now encircled by its bench; paved floor;
- foundation of the north aisle of transept, west wall (with burial chamber below).
In the ambulatory:
- east wall of the same aisle of the transept: chapel foundations.

Only one area of the Gothic collegiate church was spared (although not completely) during the conversion of the burial chambers: the choir. It was here in 1991 that excavation work revealed the remains of
a Romanesque crypt, a find which had already been expected by some specialists, although it is not mentioned at all in ancient texts. (SEE ILLUSTRATION)

Since the end of 1991, excavations have been dug methodically between the Romanesque columns and pillars down to ground level - intact despite the filling work of 1225; excavations have thus uncovered traces of circulation which stopped at that time. The elevations reach heights of almost 1.7 metres. The plasterwork - most of it still intact - is covered in places with lightly scored graffiti. Traces of wall paintings can be seen slightly further on. Both aisles of this miniature church are largely filled by the foundations supporting the columns of the Gothic choir, although they are still relatively easy to make out on either side. Missing here are the vaults and, to the east, the apse which was demolished in the 14th century to make way for the tomb of John II, Duke of Brabant. Although the Romanesque ruins have suffered, the damage is much lighter here than elsewhere: they provide us with by far and away the most accurate evidence of what the original collegiate church of Brussels must once have looked like.

Now that the whole site has been cleared of the ballast, the sheer architectural power of its noble foundations is there to be admired. In the centre there are four sombre-looking monolithic columns; the architectural features around them are white without exception; to the west, a transverse wall, running alongside which there is a series of accentuated pilasters; to the north and south stands a cruciform pillar; to the east, two large sections of wall stand opposite one another in the longitudinal axis: they once led to the lost apse. (SEE ILLUSTRATION)