Volunteers unearthed the striking 2,000-year-old piece during work at a fort in Northumberland.
The latest finds on Hadrian's Wall include a ring, hairpins and signs of game counter production.
The man, aged in his 70s, was driving a Mercedes car which crashed with an HGV, police say.
The driver of the car is in critical but stable condition, Northumbria Police say.
A car and lorry were in collision on the A69 at Greenhead on Wednesday morning.
