The west façade, which is the later part of the building, shows the complex flying buttress system on either side (535) which extends all round.

Three types of systems are currently in wide use: lashing systems, locking systems, and buttress systems.

The buttress system, used on some large container ships, uses a system of large towers attached to the ship at both ends of each cargo hold.

Because of the flying buttress system, it became possible to construct thinner walls as time passed instead of increasing the thickness to offset the large windows and higher vaults.

In architectural terms this is evidenced in the smaller, narrower windows, lack of intricate tracery or coloured glass, the almost total lack of development of the flying buttress system, the poverty of decoration in sculpture and carving.

Flying buttress systems have two key components - a massive vertical masonry block (the buttress) on the outside of the building and a segmental or quadrant arch bridging the gap between that buttress and the wall (the 'flyer').

As the buttressing systems of early Gothic architecture reduced the structural need for broad expanses of thick walls, window openings grew progressively larger and instead of having just one very large window per bay division (which would create problems with supporting the glass), the typical early-Gothic 'twin lancet plus oculus' form of plate tracery developed.