N-S running wall of roughly worked/unworked tufo and basalt boulders. Cut on N by drainage channel 4002 and on S by unknown action. Abutted on W by glariat road surface 4027. E face fully exposed with max 2 courses preserved. On E and extending below bottom of wall is a cluster of tufo and basalt that may be a collapse/rubble or perhaps the wall foundation (though this seems less likely). Served as part of E retaining wall of road (in line with 2080 to N and 4023 to S), though most likely a later construction belonging to the latest preserved phases of the road.