 Historically, and especially in Victorian times, gazetteers and cartographers insisted that the entire river was correctly named the Isis from its source down to Dorchester on Thames and that only from this point, where the river meets the Thame and becomes the "Thame-isis" (supposedly subsequently abbreviated to Thames) should it be so called.Ordnance Survey maps still label the Thames as "River Thames or Isis" down to Dorchester.Since the early 20th century this distinction has been lost in common usage outside of Oxford, and some historians suggest the name "Isis" is nothing more than a truncation of "Tamesis", the Latin name for the Thames.