 Godwin suggests that roddons were formed in the Romano-British age (AD 43–500) during a second and less severe marine incursion, which left extensive silt deposits on the seaward parts of the fens and "silt deposition up the main rivers", forming raised banks or levees.Dinah Smith agrees with Fowler, suggesting that the raised nature of the silt banks are due to the "subsidence" of the surrounding area, mainly caused by human activity, such as agriculture and drainage.These have permanently changed the environment, and future marine incursions may not have the same effects as historical ones.