Akeman Street ran from Ermine Street through the area to the west of the modern town, on through the Roman settlement to the Isle of Ely. Crossing it at Castle Hill was the road from Colchester, the Via Devana, which ran through to Godmanchester and eventually to Chester (this is now Hills Road to Huntington Road). These two routes lie along river terraces of branches of the River Granta - see "Hills". (The Trumpington Street - Kings Parade axis probably formed as the London road in Anglo-Saxon times.)
This was the only convenient route for travel from East Anglia to the Midlands & North, avoiding the impassable marshy Fenland.
The town was a major commercial port, being at the head of the navigation of the River Granta and also the only convenient river crossing point for many miles.
The Celtic name for the river is Rea (water) and some maps still show the upper part of the river as "the River Cam or Rhee".