The fortifications suffered extensive damage during sieges in 1792, 1815, and 1871 and severe destruction during bombardments in August 1914.
The popular choice for restoration is to preserve the current layout of the fortifications.
The facings have been damaged on several occasions, at times severely, since they were constructed by Vauban.
The stronghold has thus had to adapt to both good and bad developments in the art of war, from the campaigns of Louis 14th up to the Second World War. Therefore, the problem that arises is how to retain all of these layers of history whilst ensuring strict conservation of the ramparts.
Hence, the bossed facings that disappeared when the breaches collapsed will be restored to their original state.
The dressed stone which was heavily damaged by pieces of shrapnel will either be replaced entirely or in part by inserting plugs. Stones that can be conserved with no risk will be kept in their current condition thus serving as evidence but will be returned to their original position. Areas of repair following sieges or more recent restoration work will be conserved if their current condition allows.