Castle Matrix in County Limerick.

The earls of Desmond were the original builders of this fifteenth century 24.4 Meter (80 ft) stepped battlement tower house, situated on the banks of the river Deel.

After the failure of the 1580 Desmond rebellion, the castle came into the hands of Henry Billingsley, later it was purchased by Sir John Dowdall. Eventually the property came into the possession of the Southwell family one of whose defendants, John Southwell Brown added a two storey dwelling in the early nineteenth century. It was restored again in the 1970's and furnished with many antiques.

The building is now the headquarters Irish International Arts center and the heraldry Society of Ireland.

In 1580 Sir Walter Raleigh met the poet Edmund Spenser in Castle Matrix. It is claimed Lord Southwell, was presented with potatoes by Raleigh and he became the first man to grow them in Ireland. Although Killua Castle in County Westmeath is the generally the accepted holder of this distinction.