The river is the one the A151 crosses at Corby Glen and Edenham. Here the two parts are combined. Beyond the Glen, to the south, is an area of dense Romano-British occupation. On this side, a little is known but if there is more, it is covered with post-Roman marine silt(14). It looks as though this part of the river began as a single sea bank, keeping the tide out of Pinchbeck South Fen but allowing it into the lower part of that area behind the townland to the north of the road. In the late Roman or early post-Roman period, the Glen escaped from its artificial Roman course of which the Bourne Old Ea was part. (The road follows the bank of this while leaving Bourne) and found its way to these tidal flats. Later, at some early but unknown medieval date, the marsh was turned into a polder of sorts and the Glen was directed along the old sea bank which then became one of the river banks. Thus, the course of the road was determined ultimately, by that of the sea bank.