Interesting. Rochester was a major (for the time) settlement prior to the Romans arriving. The traditional tale is that they followed the major trackway which eventually became Watling Street, rather than the modern Pilgrim's Way. However arriving at the Rochester ford/ferry site they were faced with good land in Rochester but marsh opposite, where modern Strood is. The crossing of the Medway would have been possible using swimmers (auxiliaries trained to swim in full kit using bladders for buoyancy) and boats under the protective fire of ballistae and onagers. However, it would have been expensive in terms of casualties, since the Britons were encamped at the foot of Strood Hill with defensive positions on Frindsbury and Sundridge Hills. Virtually all battles in the ancient world were decided within the day, but the Battle of the Medway is notable for being possibly the first two day battle recorded in history. Some details were recorded by Cassius Dio contemporaneously. The first day ended in stalemate, Romans in Rochester and Britons still in Strood.
Accounts here differ. Some assume that the second day was a re-run of the first, but with a successful crossing. Others have a detachment of Romans, possibly the XI Hispania under Gnaeus Hosidius Geta, moving upriver under cover of darkness and fording at (possibly) Burham. The detachment then moved down river and in the morning (when?) attacked the defenders at Sundridge. Gnaeus was nearly captured, but the troops rallied and succeeded. They were then in a position to fall upon the rear of the Britons, and thereby open the way for the main force (Legio II Augusta) under Vespasian to cross the river and decide the battle.
After the battle the defenders retreated to the Thames, but subsequently a series of crossings were forced, both from the Kentish marshes and from a ford in London. Again, that is a matter of dispute, the site of either London Bridge or Westminster Bridge might have been the lowest fording point.
