it cuts through the North Downs, they constitute the most southeasterly group of megalithic monuments in the British Isles, and the only megalithic group in eastern England. The Medway Megaliths can be divided into two clusters between and apart: one to the west of the River Medway and the other on Blue Bell Hill to the east. Addington Long Barrow is part of the western group, which also includes Coldrum Long Barrow and Chestnuts Long Barrow. The eastern group consists of Smythe's Megalith, Kit's Coty House, and Little Kit's Coty House, while various stones on the eastern side of the river, most notably the Coffin Stone and White Horse Stone, may also have been parts of such structures. It is not known if they were all built at the same time, or whether they were constructed in succession; nor is it known if they each served the same function or whether there was a hierarchy in their usage. The Medway long barrows all conformed to the same general design plan, and are all aligned on an east to west axis. Each had a stone chamber at the eastern end of the mound, and they each probably had a stone facade flanking the entrance. They had internal heights of up to , making them taller than most other chambered long barrows in Britain. The chambers were constructed from sarsen, a dense, hard, and durable stone that occurs naturally throughout Kent, having formed out of sand from the Eocene epoch. Early Neolithic builders would have selected blocks from the local area, and then transported them to the site of the monument to be erected. These common architectural features among the Medway Megaliths indicate a strong regional cohesion with no direct parallels elsewhere in the British Isles. Nevertheless, as with other regional groupings of Early Neolithic long barrows—such as the Cotswold-Severn group in south-western Britain—there are also various idiosyncrasies in the different monuments, such as Coldrum's rectilinear shape, the Chestnut Long Barrow's facade, and the long, thin mounds at Addington and Kit's Coty. These variations might have been caused by the tombs being altered and adapted over the course of their use; in this scenario, the monuments would be composite structures. The Medway Megaliths' builders were probably influenced by pre-existing tomb-shrines elsewhere that they were aware of. Whether the builders had grown up locally, or moved into the Medway area from elsewhere is