From an article in the St Albans Observer by Claire Ling:
A rare coin that was made in St Albans 2,000 years ago is expected to fetch up to £1,300 when it goes up for auction in London. The Iron Age coin was struck in Verulamium [sic] between 10BC and 25 BC and horse-riding Celtic warriors are depicted.
From the Proceedings of the Society of Antiquaries of London, v3 (1856) - strange sounding barrow-like and subterranean excavations up on Therfield Heath. In all likelihood not as old as the barrows? - although flint tools were found in one, interestingly. But maybe inspired by them and their location?