The Frome Hoard, a pot-bellied Roman jar stuffed with 52,503 coins,has found a permanent home in the county where it was discovered, the Somerset County Museum at Taunton Castle which reopens to the public after a £7m revamp.

When hospital chef Dave Crisp found the hoard last year with a second-hand metal detector, the largest collection ever found in a single container in Britain, the news went round the world.

The museum has acquired the entire hoard for £320,000 – with a grant from the National Heritage Memorial Fund – but coin experts, conservators and historians will be poring over some of the coins for years to come. Some have been cleaned so they shine like gold, but though many are exceptionally rare, including a unique group minted for Carausius, a Roman general who responded to a charge of embezzlement by having himself declared emperor, and lasted three years before being murdered by his chancellor – they are mostly grimy-green-streaked copper alloy, with a scattering of silver. Thousands are still corroded into lumps which will be teased apart by conservators before the experts can examine them.

The renovation of the museum opens up many rooms in the medieval castle, which has also served as a court house, scene of the Bloody Assizes where Judge Jeffreys condemned 144 local men and women to death for their part in the Monmouth Rebellion in 1685. It has been a museum since it was bought in the 19th century by the Somerset Archaeological and Natural History Society.

The new galleries include a spectacular redisplay of the Low Ham mosaic telling the story of Dido and Aeneas from Virgil, the earliest example of narrative art in Britain – "a graphic novel from 350AD," museum director Steve Minnitt said.

Many objects will be on display for the first time, including a Plesiosaur fossil skeleton found in 2003, the first complete skeleton found in more than a century; part of a stone cross which once stood on the summit of Glastonbury Tor; and a tent-peg-like piece of crudely carved wood which is another treasure of international importance – 4,500 years old, preserved by the mud of the Somerset Levels, the earliest representation of a human figure found in Britain.