Construction of cathedrals before the 1200's consisted of supporting the upper structure with a broad base below. That is why you see such a large, deep doorway. The foundation stones were sometimes 4-5 feet deep in order to support the structure. This form of architecture began in the 800-1100 time frame, and is called Romanesque. Romanesque changed to Baroque architecture style after 1100. In the story of the Pied Piper, which covers the time of 1212 (Children's Crusade) to the time of the story, 1284 - many of the Romanesque churchs would have been standing in 1284 and still in use.

The interior of the church was open, without seating except for some benches along the wall. The public came into the large cross shaped interior and stood in groups to hear the mass sung in Latin, and they could also walk along the outer walls and visit the Stations of the Cross. Pilgrims would often enter a side door of the church, walk around the entire rim of the interior, visiting the Stations of the Cross, and never interrupt the mass.

Source
World Book CD-ROM, 2002 World Book Inc., Chicago, IL.