IT is the iconic image of Colchester. Oxford and Cambridge have their universities, York has its minster, and Colchester’s pride and joy is its castle.

Archaeologist Philip Crummy says the Norman fortress “defines” the town.

And the castle is celebrating 150 years of being open to the public. What started as a collection in a single room has expanded until the entire castle was made accessible as a museum.

Now it is one of Colchester’s top tourist attractions.

In 1855, the owner of the castle, Charles Gray Round, allowed part of it to be used as a town museum. It opened to the public on September 27, 1860, housed in a room known as the crypt.

Some of the most important collections acquired over the years include the Acton Collection, which is made up of archaeological material collated in 1840 by archaeological pioneer William Wire, and the Jarmin Collection of Roman artefacts from Colchester. The Jarmin Collection includes the tombstone of Marcus Favonius Facilis, a centurion of the 20th Legion.

Peter Berridge, Colchester and Ipswich Museum Service manager, said: “By the end of the 19th century, Colchester Castle contained what was probably the finest and most extensive collection of British Roman material existing at the time.”

Money donated by Viscount Cowdray, who had been MP of Colchester, was used to buy the castle for the borough in 1920.

In 1926, the collections from the Essex Archaeologist Society were amalgamated with Colchester Council’s collection. Then in the 1930s, the collections were added to with Iron Age and early Roman objects from excavations from the Sheepen area of Colchester.

Philip Crummy, director of the Colchester Archaeological Trust, said: “A visit to the castle museum is a drop-dead must for anybody with even the remotest of interest in Roman Britain and Norman castles.

“Its remarkable collection is a product of gifts and purchases, which we cherish for the future. It helps define modern Colchester and its place in Britain today.”

Colchester mayor Sonia Lewis added: “The museums and Colchester Castle are to be congratulated on 150 years of excellence. I would like to thank all staff who work hard setting out exhibits, keeping the castle attractive and making visitors welcome.”

There is a small display at the castle to mark the 150th anniversary. It contains objects originally displayed in the castle in a 1960s centenary exhibition.

The exhibition includes items from the Henry Vint, Acton and Josalin collections, as well as the original accession register.

There are pen and ink drawings of the castle from 1849, before it became a museum, and an unusual early specimen of a crab from the natural history collection, which had oysters growing on its shell.

A limited edition 150th anniversary mug will be available at the castle shop for the rest of the year.

l The castle museum is open Monday to Saturday, 10am to 5pm, and Sunday, 11am to 5pm.

For more information, visit colchestermuseums.org.uk