the witham, which was originally tidal up to lincoln, was an important navigation in roman times. lincoln (lindum)—the meeting point of ermine street, joining london to york, and fosse way, leading to leicester and bath—was an important roman fort that became one of only four colonia in britain. most important roman cities were situated near navigable water, which enabled goods to be transported in bulk, but lincoln did not possess this advantage, and so the romans constructed the fossdyke from lincoln to torksey on the river trent, improved the river witham from lincoln to the wash, and built the car dyke from lincoln to the river cam near cambridge. the witham thus gave lincoln access to the east coast, while the fossdyke gave access to the trent and further on to the humber.