On Caesar's second invasion attempt in 54 BCE, Cassivellaunus led the British defensive forces.The Romans besieged him at Wheathampstead, and partly because of the defection of the Trinovantes (whose King Cassivellaunus had had murdered), the Catuvellauni were forced to surrender. Alban, a Roman army officer who became Britain's first Christian martyr after his arrest at Chantry Island, died in the 3rd or 4th century and gave his name to the modern town of St Albans.There is considerable evidence of a mint in Hertford at this period.Edward the Martyr (from 975 to 978), Æthelred the Unready (from 978 to 1016) and Knut the Great (from 1016 to 1035) all had coins struck there.Nevertheless, just south of present-day Ware and Hertford there is some evidence of an increase in the population, with typical round huts and farming activity having been found at a site called Foxholes Farm.In the Iron age, a Celtic tribe called the Catuvellauni occupied Hertfordshire.Later, Ermine Street would be built directly on top of it.It was at this Synod that the "question of Easter" was settled, and the church agreed how to calculate the date of Easter.
In the 19th century, rail links sprang up in the county, linking London to the north.
Hatfield in Hertfordshire has seen two rail crashes of international importance (in 18).
Though nowadays Hertfordshire tends to be politically conservative, historically it was the site of a number of uprisings against the Crown, particularly in the First Barons' War, the Peasants' Revolt, the Wars of the Roses and the English Civil War.
A number of Roman Roads run through Hertfordshire including Watling Street and Ermine Street.
The ancient trackway, the Icknield Way also runs through Hertfordshire.The Synod also marked the end of the conflict between the Celtic Church and the Romanised church introduced by Saint Augustine.