The lands of Mugdock were a property of the Grahams from the mid-13th century, when David de Graham of Dundaff acquired them from the Earl of Lennox. It is possible that the castle was built by his descendant, Sir David de Graham (d. 1376), or by his son in 1372. In 1458, the lands were erected into the Barony of Mugdock. Later, in 1505, the Grahams were created Earls of Montrose.
The original castle may have been shield-shaped on plan, comprising towers arranged around a courtyard, and linked by curtain walls and ranges of buildings. The castle stood on a natural, steep-sided mound formed of hard volcanic rock. Of the early castle, only the south-west tower remains complete, and forms the most recognisable feature of the ruins. The narrow tower is of four storeys, with an entrance on the first floor, accessed via exterior steps on the east side. Inside the basement is vaulted, and a single room occupies each storey. On the outside, a line of corbels projects the two upper storeys out from the lower levels, giving the tower a distinctive 'top-heavy' appearance. The only other remains are the basement of the north-west tower, part of the gatehouse, and linking sections of curtain wall.
The castle was extended in the mid-15th century, probably around the time that the barony was created. An outer wall was built to enclose the majority of the mound as an outer courtyard. This courtyard had its main entrance to the south, adjacent to the south-west tower. Inside the courtyard are the ruins of various stone buildings, mainly dating from the 16th century. These include a chapel at the north extent of the courtyard, and a domestic range at the south-west. Much of the outer curtain wall has also disappeared, although the southern section remains.
A terraced walled garden, incorporating a summer house, was built to the east of the castle in the 1820s. Local historian John Guthrie Smith (1834–1894), a relative of the Smith family of nearby Craigend Castle, leased the house from 1874. He had the 17th-century mansion demolished, and commissioned a Scottish baronial style house to be built in the ruins of the old castle. It was designed by architects Cambell Douglas & Sellars, and was extended to designs by James Sellars in the 1880s.
References:From its origin as a small stronghold built by the ancient Illyrian tribe Dalmatae, becoming a royal castle that was the seat of many Croatian kings, to its final development as a large fortress during the Ottoman wars in Europe, Klis Fortress has guarded the frontier, being lost and re-conquered several times. Due to its location on a pass that separates the mountains Mosor and Kozjak, the fortress served as a major source of defense in Dalmatia, especially against the Ottoman advance, and has been a key crossroad between the Mediterranean belt and the Balkan rear.
Since Duke Mislav of the Duchy of Croatia made Klis Fortress the seat of his throne in the middle of the 9th century, the fortress served as the seat of many Croatia"s rulers. The reign of his successor, Duke Trpimir I, the founder of the Croatian royal House of Trpimirović, is significant for spreading Christianity in the Duchy of Croatia.