The suffix of -chester or -cester to English towns are common indications that the place is the site of a Roman castrum, meaning a military camp or fort. The area around Chichester is believed to have played significant part during the Roman Invasion of A.D 43, as confirmed by evidence of military storage structures.
The city centre stands on the foundations of the Romano-British city of Noviomagus Reginorum, capital of the Civitas Reginorum. The Roman Road of Stane Street, connecting the city with London, started at the east gate, while the Chichester to Silchester road started from the north gate. The current plan of the city is inherited from the Romans: the North, South, East and West shopping streets radiate from the central market cross dating from medieval times.
Many typical aspects of Roman cities (walls, baths, amphitheaters) are found in Chichester. Thick Roman walls were discovered, lasting for one and half thousand years, but were then replaced by a thinner Georgian wall.
Roman baths were also found and are on display in a museum, The Novium, which preserves and showcases the remnants of the baths, as well as presentes a history of the area from pre-Roman to the twentieth century.
An amphitheatre was built outside the city walls, close to the East Gate, in around 80 AD. The area is now a park, but the site of the amphitheatre is discernible as a gentle bank approximately oval in shape.
Like many great English cities, I've visited that began as Roman towns (York, Chester, London), it never ceases to amaze me how far back English history goes. Though towns may look only a few hundred years old, they are in fact thousands of years old.