The River Lethe was one of the rivers of Hades in Greek mythology. Exposure to its waters was held to lead to loss of memory, or, more intriguingly, a state of "unmindfulness" and oblivion. From this origin, it has re-appeared throughout western culture, from Dante to Tony Banks's first solo album (River Lethe in popular culture, Wikipedia).

By providing the alternative spelling of Leith, Alasdair Roberts 'doubles' this meaning with the Water of Leith, a river that runs through Edinburgh, and co-locates ancient Greek and contemporary Scots mythology.

The idea of eternal return is bound up with memory, with cultures being compelled to repeat and confront the missteps of the past. So the oblivion of forgetfulness provided by the endless Lethe provides a form of antidote or escape.