The blog cover picture shows ‘Burrow Mump’ another of the Somerset landscape protuberances which were marsh-surrounded islands in the early Middle Ages (and real islands in the recent floods). ‘Mump’, meaning a rounded hill or hillock, seems to be a Somerset dialectal word which has been connected with other ‘-ump’ words (esp. lump clump plump hump rump bump tump) by phonosemantics. Kelston Round Tump is one name (perhaps now growing obsolete? but common in my childhood) for Kelston Round Hill, near Bath.
On the Somerset marsh map enlarged detail (see the main map on ‘How did he get there?’), Burrow Mump is that small island perched on the top right-hand corner of the Athelney light rectangle. There is no archaeological evidence that it was used in Saxon times, other than, possibly, as a strategic lookout place; never a fortress. Medieval remains (including a church or chapel) are post-Conquest to late medieval. The present ruins are of an 18th.-c. structure.