A Greek historian who served as an official in the courts of the Eastern Roman Empire. The exact dates of his birth and death are unknown but he is considered to have been a contemporary of Anastasius I (491-518 AD).
The author of a history of Rome, known as the Historia Novae or the New History, consisting of six books composed between 501 and 502 AD. (And written naturally, in Greek, that being the language of the Eastern Empire.) The work is incomplete, book six in particular is believed to be an unfinished draft and obviously ends before it is meant to. Which we can only presume is because Zosimus was prevented from completing it either by his death or some other event.
The New History begins with a brief outline of the period from Augustus up to 270 AD, and then proceeds with a more detailed history and tracks the decline in fortunes of the Roman Empire until the events immediately preceding the sack of Rome by the Goths in 410 AD. As a devoted pagan(*), he attributed the decay of the Roman Empire to the failure of the Romans to worship the old gods.
Since Zosimus often conflates and confuses different people, events and geographical locations he is generally considered to be rather a poor historian. However the value of his work derives from the fact that much of it was simply compiled from other, more dependable sources such as that of Olympiodorus. As little of Olympiodorus's original has survived, the New History serves as our next best proxy.
Zosimus is our main source for what have been seen as two key events in early British history - the Romano-British Revolt of 409 and the Honarian Rescript of 410.
(* Which in itself is worthy of note, given that Paganism had supposedly been outlawed within the Empire two centuries previously.)