The team are working with Colm Donnelly, Finbar McCormick and others from Queen's University, Dublin. Their brief is to investigate an impressive ruin in County Down, Northern Ireland. It is associated with John de Courcy and his renegade Norman knights. But when was it built, and what did it look like? As it's a protected monument, their dig is strictly limited. Francis takes charge. Colm thinks the site shows remains of a much earlier structure, a cashel or defended stone enclosure from the Dark Ages. He shows Tony the nearby Drumena Cashel. Matt demonstrates the inferiority of primitive Irish armour against the full might of a mail-clad Norman knight with his huge charger, sword and bow.