The 13th-14th century leather harness, which went around a horse’s chest and was attached to the saddle, is covered in gilt, copper-alloy shields, and boasts heraldic symbols.
It may have belonged to a medieval knight and is the only intact example ever found in Britain or Ireland.
The treasure trove of artefacts includes scores of pieces uncovered around the castle at Caherduggan, near Doneraile, Co Cork.
The finds were made by archaeological consultants commissioned by Cork County Council.
The excavations were completed in 2011 and 2012 as part of a project to remove a bend on the main Mallow-Doneraile road.
Rubicon Heritage, Ireland’s largest archaeological consultancy based in Midleton, described the site as a “most remarkable” castle.
Archaeologist Damian Shields yesterday said they had discovered a number of extremely interesting finds, the most important of which came from a medieval water well.
Among the items found were a bone dice for gaming, a medieval woman’s shoe, and one of the most important finds they had ever uncovered — the complete 13th/14th century leather horse harness known as a peytrel.
“Post-excavation analysis has revealed it is the only intact example ever found in Britain or Ireland and it may have belonged to a medieval knight or one of his retainers or retinue. It was certainly belong to someone important in the medieval period. This is a hugely significant find in Ireland.”
The heraldic shields also feature symbols of a rampant lion on its hind legs.
The archaeologists have contacted the chief herald’s office to try to determine which herald it might be. The castle belonged at different periods to the Barry, Roche and Grove families.
The excavations were carried out on an outer ditch of the castle and the water well. Evidence of a fairly large, pre-historic settlement was also found, including a marketplace at a cross roads and a fort.
The artefacts were sent to the National Museum.
Mr Shields said more excavation was needed at the castle. “I would love to go back to have another look at this site,” he said.