The earliest written references that have survived relating to the islands were made circa 77 AD by Pliny the Elder in his "Natural History", where he states that there are 30 ', and makes a separate reference to ', which Watson (1926) concludes is unequivocally the Outer Hebrides. Writing about 80 years later, in 140-150 AD, Ptolemy, drawing on the earlier naval expeditions of , writes that there are five ' (possibly meaning the Inner Hebrides) and '. Later texts in classical Latin, by writers such as , use the forms ' and '.