Good find. I always wondered why they didn't just earth ramparts ahead of thinner stone on standard forts.
Well there were different schools of tought about that.
You could go for almost entierly earth ramparts (indeed whole forts), but then you run into the risk of the fort being easier to storm by surpirse or an overwhelming force due to the slopes in earth being relatively flat.
This was the method chosen by Benno van Coehoorn, but he could in a sense get away with it because in the low countries he could provide his forts with wet ditches, thus make them essentially storm-proof;
Vauban otoh mostly had to build forts with dry ditches (there are exeptions in north west France). hence he felt the need for stone ramparts to get a fortress that was proof from being swamped by massive infantry or by surprise by a smaller force. now you have to take into account that Vauban did realise the vulnerability of masonry work to artillery. he tried always to cover the masonry walls behind detached earth works backed by masonry support (i.e. sand in front of the masonry). it is this refined interplay of stone crutain walls covered from direct fire by earthen works that form the core of the "Vauban system" , if we can call it that. The general bastioned fort principle was developed way befor Vauban, but he made them much more resistant to artilery.
In the 19th century, before the advent of concrete, we see that e.g. Brialmont elvolved his designs quickly to being stone cored structures with heavy earth cover in front (and on top of them). This general principle was later followed by Séré de Rivières in France.
there is much more to it, but i guess this gives an outline....
Edited by Inhapi, 03 February 2020 - 0731 AM.