Every Monday we will post an entry that hasn’t yet been published with a view towards harnessing the collective onomastic power of the internet. If you have any thoughts about the name’s origin, other variants it might be related to, other examples of its use, etc., please share them in the comments! If you wish to browse other Mystery Monday names, there is an index.
Early 13th-century France is not a place where you expect to find quirky, unusual names. And yet, take a look at this:
It’s from a Latin document but the nominative spelling is Alsarembers — not a typical Latin case-ending! Could it be influence of the Old French vernacular poking through? A typo in the edition? A manuscript error? Who knows!
But solving that question won’t address the deeper one, which is: What kind of a name is this? It’s certainly not your ordinary dithematic Germanic name, nor is it an easily identifiable Latin/Christian name. If anything the Al- feels Arabic.
We’d love to know if you have any thoughts. Please share in the comments!
Dictionary of Medieval Names from European Sources 
If it’s any help, the original ms. is online here:
https://gallica.bnf.fr/ark:/12148/btv1b10039072g/f104.item.r=cartulaire
It looks like Alsarẽbers to me (104r, line 3 from the bottom), but it might conceivably be a W (Warembers), or a copyist’s misreading for a W in a previous document. If so, it could be related to Vuarembertus in 21, Vuarenbert 129 (Warnbert in the dictionary).
I’m familiar enough with that hand to be quite sure that it’s Alsarēbers; that initial A is very characteristic (see for instance Apud at the beginning of the paragraph).