Portumna Castle, built near the shore of the northern extremity of Lough Derg on the river Shannon in the reign of James I, was without equal in Ireland at the time in style, grandeur and distinction - outshining castles at Rathfarnham, Kanturk, Carrickfergus, Charlemont and Burncourt. The elegance of Portumna can be attributed to the taste, experience and wealth of its builder, Richard Burke, fourth Earl of Clanricarde, Lord President of Connacht, of the famous de Burgo family of Norman extraction. It was built between 1610 and 1618 at a cost of £10,000, and the earl also built a mansion at Somerhill, Tonbridge Wells in Kent.

Portumna was one of the first, if not the first, building in the country to admit some of the Renaissance refinements already common in Italy and France for over a century, but which took so long to filter through to Ireland. The shell of this great mansion conveys an impression of alien splendour, and the overall effect is unique and has a curiously continental air. The Renaissance features of the exterior of Portumna are - strictly speaking - limited to the fine doorcase of the front entrance and the Tuscan gateway of the innermost courtyard, but the very layout is an expression of Renaissance ideas. The castle is symmetrical in shape and consists of three stories over a basement with square corner projecting towers. It measures 29.7m by 21.2m and the corner towers are 6.5m square with gunports. A central corridor, 3m wide runs longitudinally from top to bottom, supported by stone walls, which contain numerous recesses and fireplaces. The approach is elaborate from the north with gardens, avenues and three gates.

Portumna Castle, built by Richard, 4th earl of Clanricard (d.1635), is examined by historians, architectural and garden historians and archaeologists, who manage to recreate the world of this ambitious Irish courtier and the political and social context for the building of the castle. The house/castle was built against the background of Clanricard's political manoeuvrings and the process of anglicization within his lordship. Renaissance ideas, traditional skills, courtly manners, political motives and sophisticated decoration come together at Portumna Castle, as Clanricard was to introduce new skills and the latest architectural ideas in the construction of his house. But behind these aesthetic ideals lies the determination of this man to reinforce his claims to high position and ownership of huge landholdings. By its very size Portumna Castle is a manifestation of its builder's ambitions in Ireland.