Hryggjarstykki

Hryggjarstykki is a lost kings' saga written in Old Norse in the mid-twelfth century and dealing with near-contemporary events. The author was Eiríkr Oddsson, an Icelander about whom little is known. The work is cited by Snorri Sturluson in Heimskringla, where its reliability is emphasized.

Eiríkr's account is also cited in Morkinskinna in a similar manner.

The author of Fagrskinna also made use of Hryggjarstykki though he did not explicitly cite it. It has been suggested that Morkinskinna, Heimskringla and Fagrskinna made use of three different versions of Eiríkr's work.

Unlike most of the later kings' sagas Hryggjarstykki may have been an exclusively prose work, though it seems to have made some use of skaldic poetry. Earlier scholars believed the work had covered a substantial part of the 12th century, starting in the 1130s and going up to the 1160s or 1170s but more recent analysis indicates that Hryggjarstykki may only have covered the years 1136-1139. Its time of composition would then be around 1150, possibly making it the earliest saga.

...
Wikipedia