"These buildings were erected by highly skilled labourers and master of various guilds"
No they weren't - the intricate work may be carried out by artisans and craftsmen (who were very much a part of the labouring classes - certainly not princes, Dukes, Bishops, merchants...) but the heavy lifting was done by unskilled labour - no diffrent from any other job requiring a mixture of skilled, semi-skilled and unskilled labour.
Jim Carroll