The German prefix ur- is roughly "proto-", "primitive", "original". (also borrowed into Scandinavian languages and as 'oer-' in Dutch) So alt is old while uralt is really old. (and through that has been generalized into an intensifier, as in urgemütlich! - 'super cosy!')

So - Proto-germanic is Urgermanisch. Ancient prehistory is Urzeit (ur-time), Ursprung - origin (the ur from which something has sprung, I guess you could say), Urheimat - ancestral homeland or place of origin of a people (Heimat meaning homeland), protoplasm is Urschleim (Ur-Slime; a term that should totally be used in English) and a prototype as in the original form of something, is an Urtyp (although 'Prototyp' is the more common word in most cases where 'prototype' is used in English) It's got no relation to Ur in Babylon but the latter does have an appropriate name if you ask Germans.

So "ur-history" is the most ancient history of something and/or the history of the origin of something. The prefix has been borrowed into English but it's most commonly seen in linguistic contexts ("urtext", "urlanguage" etc)