The Slad is the name given to an Iron age defensive earth rampart in Hertfordshire, England. It is thought to have formed part of a defensive fortification, joining up with the Devil's Dyke and bordered on the north side by the River Lea to create a fortified enclosed settlement of approximately 35 hectares (86 acres).
It was constructed towards the end of the Iron Age, and probably in the early 1st century AD. This, and other similar earthworks in the district, were built by the powerful Celtic tribe established in this area, the Catuvellauni, to define areas of land around their tribal centre at Verlamion – the predecessor of the Roman city of Verulamium.
Unlike Devil's Dyke, the Slad is located on private property, and is not accessible to the public.