The Romans and Anglo Saxons
The Romans probably had a ford and ferry across the river just to the right of Chertsey bridge going out of the town. In ancient times the river was lower when out of flood.
It was here that the wooden medieval bridge was built and evoked the poem by John Taylor, The ‘Water Poet’, (1580-1653).
“Tumbling ‘twixt Middlesex and Surrey land,
We come to Chertseyes crooked bridge doth stand;
Which fore was made all by left-handed men
The like of it was never in my Ken”:
Back in the town up off the flood plain, it is extremely possible that there was a dwelling built around the late Roman or post Roman period. This would be situated on the highest ground which is now Abbey Gardens. Perhaps it belonged to one Cerotus. (‘Cerotus Isle’) However, there is no real archaeological evidence for this, yet.
Formal documented history in this area starts with the building of the Saxon Abbey in Abbey Gardens. The traditional date for the start of this building is 666 AD but actually more likely to have been 671. 
This Abbey was built on the highest possible ground so as to keep the monks feet dry all year round, a real consideration in the days before the invention of vulcanised rubber for footwear and when the local area round about regularly flooded in the winter. The closeted northern cleric the Venerable Bede (731) refers to an Abbey at ‘Ceorteseig’, the Isle of Cerotus. At some point this modest wooden monastic foundation would have very likely become stone built as modern archaeology suggests.
The Benedictine Abbey was sacked in 871 by Viking raiders coming up the Thames, and again sometimes later when there was much killing and burning. A sword from this general period was found close by a little further up the Thames in a gravel pit in 1981. The finder was Mixham’s gravel worker Harry Cooper. This handsome weapon made by one ULFBERT is now displayed in our Museum after Mr Cooper, (prompted by his wife), bought it to the Museum late one Wednesday afternoon in wrapped in a popular Sunday newspaper.