(17) Four tumuli at Barlow Hills, Essex; (18) Gallery of the largest.
Presumably the plate was made for another publication, since this is marked as figure 21 and not 17 or 18.
This is said to be the largest barrow in Britain, and, until the railway destroyed three of the mounds, the largest group in Europe. The largest is some fifteen metres (14 feet) high.
These Romano-British remains probably date to the second century AD, and are Roman rather than Druidical in nature. They are on the border between Essex and Cambridgeshire.