Montmorency blade in late 18th c. British military swords

[Hotspur]

In my opinion, the fullers at the spine are to add stiffness, even though the Bancal was known to fold.

Not limited to sabres, here is a German backsword blades about 1800 and a 1750ish Germanic hussar hiltsabre with a wider spine fuller, as we see on British stuff after 1780.

Cheers
GC