An Iron Age or early medieval promontory fort which may have been occupied in the 5th - 6th century AD. It is situated on a natural promontory above the Santon River. It utilises almost vertical drops to the north and west for protection and is defended to the south and east by an earthwork rampart with a maximum internal height of 1.7 metres. An outer ditch on the landward side is now almost ploughed out, but the remaining portion has a maximum width of 5.0 metres. The maximum depth from the outer lip is 1.1 metres with the drop from the top of the periphery bank 2.5 metres. The bank has several probably modern breaks on the landward side but no original entrance could be detected. The fort is grass-covered and no trace of internal habitations was found.

Medieval longhouse. Prior to investigation in 1957, there were clear surface indications of a building in the interior of the fort, but excavation proved it to be rectangular and orientated NW-SE, with bowed walls and internal measurements of 7.5m by 4m. There was a possible entrance 2m wide in the south-east corner, but no trace of stonework. Another possible entrance pierced the wall on the north-east, though this lay perilously close to the cliff edge. Apart from a few postholes for support for the roof and entrance, little else survived to indicate the construction of the walls, which seem to have been of earth and turf. There was a rudimentary raised bench along each long wall and at the west gable, formed by cutting down into the bedrock in the centre of the building. There were also signs of a central hearth, though this took the form of burnt material rather than a built structure. The excavator believed that the house represented Medieval reoccupation of the site.

Medieval watch place. The rudimentary construction of the medieval building, the lack of a hearth structure and the paucity of domestic rubbish has led to the site's reinterpretation as a place from which a coastal watch was kept - 'watch and ward' - and did not serve a domestic purpose.

Prehistoric flint scatter. A small quantity of worked prehistoric flint was recovered from Cass Struan by CH Cowley. No further details concerning the circumstances of the discovery were recorded and the grid reference relates to the point at which the watercourse reaches the beach for indicative purposes only. The antiquary Charles Harry Cowley was an avid collector of worked flint and coarse stone artefacts revealed by agricultural activity, mainly on farms located around Peel, and occasionally from further afield. He was active from 1900 until 1943. His entire collection of artefacts, together with a daybook cataloguing his discoveries, was later donated to Manx National Heritage.

Prehistoric flint scatter. A single worked prehistoric flint was recovered from 'the Brooghs between Cass Struan and Whitestrand' by CH Cowley. No further details concerning the circumstances of the discovery were recorded and the grid reference relates to the clifftop midway between the two beaches for indicative purposes only. The antiquary Charles Harry Cowley was an avid collector of worked flint and coarse stone artefacts revealed by agricultural activity, mainly on farms located around Peel, and occasionally from further afield. He was active from 1900 until 1943. His entire collection of artefacts, together with a daybook cataloguing his discoveries, was later donated to Manx National Heritage.

The original square stone building of the Castle Mona Hotel consisted of two three storey wings front and back joined by a two storey 'link' of similar plan size. The flat roofs of the wings are concealed behind parapets decorated with roundels and garland motifs except over the entrance where castellations indicate the substantial protruding porch with its columns and wrought iron balustrade to a flat roof. The central link has a slate pitched roof visible through a castellated parapet. The well proportioned rectangular windows decrease in their vertical dimension with each succeeding storey but receive the same treatment on all elevations of the structure. The building is crowned by a circular castellated tower rising from the rear of the main facades toward Douglas bay. A recent extension to the sea creates a large terrace with wrought iron balustrade on the roof of the single storey alteration which is fronted by shops onto the main pavement of the Cresent. No interior inspection has been made. Although the developments of the promenades at Douglas has detracted from the siting of Castle Mona by leaving it behind the main visual facade, the building is still impressive both for its quality of architecture and its historic significance as the early residence of the Duke of Atholl (Governor General of the island 1793-1830).

The royal castle at Castletown, seat of the Lords of Mann since the Norse period. A limestone fortress that has served as royal residence, garrison, prison, and seat of government across eight centuries. The castle the Lords held, the Governors occupied, and the Crown inherited. Its continuous use across every period of the Island's history makes it the physical thread connecting the Norse kings to the modern Crown dependency.

For much of the 19th century (1813-91) the keep was the focus of prison activity whilst the castle served as the Island's main gaol. Major alterations included the insertion of a stairwell within the SW corner and various breaches through the walls to reach new accommodation blocks and exercise yards constructed within the inner bailey. Some of these changes were restored once the castle ceased to be a prison, during a restoration programme conducted under Lt Governor Lord Raglan between 1904-10.

Medieval mantlet. The keep was strengthened in the first half of the 14th century by the addition of a drawbridge and mantlet protecting an entrance facing north and inland along the west bank of the Silverburn. It is thought that a small bailey may have been attached, which is reflected in the layout of nearby streets in the modern town.

Medieval gatehouse. The gatehouse was added in the mid- to late- 14th century, as part of the gradual development of a curtain wall circuit around the keep.

Modern courthouse. The upper level of the gatehouse served as a courthouse until the early 21st century, preserving administrative and judicial functions connected with the castle as the gubernatorial seat, and the surrounding town as the Island's capital until the late 19th century.

Medieval curtain wall. The castle's defences were gradually strengthened and extended through the 14th century by the development of a curtain wall circuit protecting the keep. Development began with the early construction of the mantlet, and continued in an anticlockwise direction culminating in the development of the outer gatehouse and eventually the barbican. From as early as the third quarter of the 14th century the curtain wall defences included provision of artillery, positioned in turrets.

Post medieval barbican. The barbican was developed from the 14th through to the 16th century. Its masonry shows a varied development history, complicated by the scars left after the removal of a police station around the turn of the 20th century.

Post medieval counterscarp and glacis. During the second quarter of the 16th century, protection of the curtain wall against artillery was provided on the east and south sides by the addition of a counterscarp wall faced with a glacis. Now covered in turf, the glacis was originally faced in stone.

Medieval stone castle. Castle Rushen is widely regarded as one of the most complete medieval fortresses in Europe. It was begun by the Norse kings of Man in the later 12th century, probably by Reginald (1187-1226), though its form was influenced by Anglo-Norman design. It was captured by Robert Bruce during a Scottish raid in 1313 that was intended to frustrate English activity in the Irish Sea, but seems to have undergone repair and significant development soon after. In 1417 it was the location for a Tynwald assembly and again in 1422 for an assembly held before Sir John Stanley, the new English overlord. At this time it had attained its modern height and a curtain wall had been added. By the 16th century further development had taken place, transforming it into an artillery fortress protected against cannon-fire by an outer glacis. In the mid 17th century the castle was refortified by James Stanley the 7th Earl of Derby as part of his defence of the Island against Parliamentary forces. In spite of this the castle fell due to a rebellion by the Manx against the Stanley family in 1651 in the face of a threatened siege by Parliamentary forces. More recently the castle served a more administrative function, acting as the governor's residence and as a prison. In the early 1900s the many late accretions resulting from its development as a prison were removed, restoring it to some of its former glory as a medieval fortress and the seat of kings whose power held sway over the Irish Sea and the Western Isles of Scotland.

A mint was operating at Castle Rushen from 1733 onwards.

Post medieval round tower. The south and east-facing aspects of the outer glacis were once strengthened at this point by the presence of a substantial tower, now demolished to below ground level as a consequence of road widening.

Post medieval tower. The approach to the castle from the north was protected from the early 16th century by the construction of an outer artillery tower. Unlike the other outer defensive strongpoints constructed in this period, the Round Tower was not physically connected or incorporated in the glacis.

Modern harbour breakwater. The outer breakwater at Castletown was begun in 1844 and completed in 1845, by the Island's Harbour Commissioners. The cost was £2,700, and its construction created the New Basin, sometimes known as the 'dry harbour'. Its creation was criticised in an offical report published in 1845 as 'unnecessary', and was stated not to have been built in line with the recommendations of engineers or local fishermen and pilots. The breakwater was extended by 30 yards in 1849, and marked with a masonry beacon. Its total length is 185m.

Modern brewery. The Ordnance Survey 1:2500 First Edition mapping of 1868 shows a brewery centred at this location. Brewing appears to have been conducted at the site for several decades prior to this. The brewery complex ceased operation in 1986, and was demolished in readiness for a residential redevelopment which was completed a few years later. The site, and the road alongside, is now known as Brewery Wharf.

Modern brickworks. Although Bagnio House has been identified by means of an inventory of Castle Rushen made in 1694 as the site of a 17th century brick kiln owned by the Lord of Man, the persistence long after of a field name at Red Gap farm suggests that brickmaking could have continued for some time after this period. The field was still known in the 1820s as 'the Brickfield', implying that here the clay was dug for brickmaking. The farmstead lay at the grid reference provided, some 600m WNW of Bagnio House. The site has been altered by road-widening.

A bridge at Castletown Harbour.

Modern road bridge. The modern concrete and steel road bridge carries traffic into the old medieval part of the town. It stands on the site of several previous bridges, and makes use of the adapted abutments and central pier of its immediate predecessor, which operated as a swing bridge.

Modern bridge. The modern road bridge and integral footbridge on its downstream side cross the Silver Burn just downstream of the railway bridge. The bridge carries the modern bypass road (A5) which avoids the centre of the medieval town. A plaque recording its construction is placed on its westerly end.

A post-medieval bridge recorded in Castletown.