Trinovantum (Latin: New Troy) refers to the capital city of the Trinovantes tribe of Celts who settled along the banks of the River Thames before the time of the Roman conquest of Britain. Its name serves as the basis for Geoffrey of Monmouth's theory that Britain was settled by Trojans following the Trojan War. Although historian's doubt the existence of such a city before the Romans occupied Britain, Geoffrey claims that Trinovantum is the name of the city of London before King Lud rebuilt the city and named it after himself.

This legend is included in the Matter of Britain.