The Car Dyke and the Foss Dyke

Lincoln, the Lindum Colonia of the Romans, is on the top of a hill overlooking the point at which the river Witham, having flowed northwards parallel to the Lincoln Edge, turns sharply east and then runs south-east to enter The Wash below Boston.

Wher the river turns east below Lindum Hill it widens out to form the Brayford Pool. This is believed to be the oldest inland harbour in the country, used sine Roman times. Linked to it are two significant waterways that apparently date from Roman times. I was recently reminded of their long history by an online article from Cambridgeshire Live which can be seen at Ancient waterway built by Romans that runs for miles throughout Cambridgeshire

The Car Dyke runs almost sixty miles from Washingborough, which lies on the Witham three miles east of Lincoln, south to the Soke of Peterborough, and then further south to Waterbeach on the river Cam. It may have been created both for drainage and transport. Wikipedia has an article with considerable detail at 

Car_Dyke

If the Car Dyke helped to link Lincoln and the coast and the waterways to the south, then by creating a link from the Brayford Pool to the Trent at Torksey the Romans ( or if not them King Henry I) linked the city to the north midland river system around which the Trent. Wikipedia has another, similar, article at Foss_Dyke

I would consider them both to be Roman, if maybe given a makeover by the Normans, and a crucial part of the network of waterways that linked East Anglia, Lincolnshire, and southern Yorkshire throughout the medieval centuries.