agger

noun2

1. •
   A double tide, particularly a high tide in which the water rises to a given level, recedes, and then rises again (or only the second of these high waters), but sometimes equally a low tide in which the water recedes to a given level, rises, and then recedes again
2. •
   (historical) Synonym of earthwork in ancient Roman contexts, particularly a defensive wall or mound.

   • By the Augustan period, however, the old ashlar circuit with its earthen agger was beginning to be dismantled in some places. — 2012