 These are arranged into lettered series according to the scheme of Stuart Rigold, devised in the 1960s and 70s, and sometimes by the numbers applied to types in the British Museum catalogues of the 1880s and expanded thereafter to around 150 different varieties.The current chronology, basically laid down by Mark Blackburn in the mid-1980s, rests on the large Cimiez hoard from southern Gaul, which contained "sceattas" of several secondary types alongside local issues of named rulers that allowed the hoard to be dated c. 715/20.There remains much uncertainty about the organisation behind the "sceattas" and exactly what authorities lay behind minting.