The monument consists of a round tower part of a larger building, the bulk of which lay to the SW of the tower. The tower now seves as an 'eye-catcher' in the grounds of Asloun House.
There are few records of the history or ownership of the site, although it is thought to have been built for a branch of the Calder family, later passing to the Forbes family. A charter of 1563 confirmed in the Register of the Great Seal, with 'John Cowdell de Asslowne' as a signatory, suggests a date before which the castle had eben built.
According to the 'Statistical Account of Scotland' of 1795, the greater part of the Castle was demolished in the mid-18th century. A plan of the castle published in 1921, when more of the walling was to be seen, shows the main block as having had dimensions of about 12m N-S and 15m E-W, with a vaulted ground floor divided into two compartments. There is likely to have been a principal courtyard to the south, since the main entrance appears to have been on the southern side of the surviving tower.
The tower rises through four storeys. The entrance doorway, which has rebates for a door and yett, is framed by a heavy quirked roll moulding; above the lintel of the doorway the wall is flattened for some distance up to a short section of string course, where it again becomes curved. The walls are pierced by windows of a variety of forms, and by circular shot-holes within oval frames, one of which is elaborated by ogee flips above and below. There is also provision for a number of armorial tablets (one heraldic stone is now reset in the steading to the west). At about two-thirds of its height there is a string course, and there may have been a corbel table at the wall head; there may also have been a dormer gablet supported by more prominent corbels. Internally the lower two storeys of the tower of the tower contained a stair to the principal rooms on the first floor of the main block (only the stubs of the stair remain), and those two storeys are covered by a flattened domical vault. The two upper storeys were evidently treated as individual chambers, and there was presumably a garret within a conical roof. The stair to the upper floors was in a turret corbelled out in the angle between the tower and the main block.
Of the main block the only upstanding remains are a stretch of the lower storey of the north wall and the stub of the east wall. The former embodies two slit windows with splayed internal embrasures, together with the jamb of a doorway that would have opened between the two rooms at ground-floor level. There are traces of a segmental vault over the E ground-floor chamber. The tower was consolidated in the 1960s, at which time the lintel of the doorway appears to have been replaced.
The area to be scheduled has maximum dimensions of 22m from W to E and 34m from N to S as marked in red on the accompanying map extract.
Statement of National Importance
The monument's historical significance can be characterised on the following criteria:
INTRINSIC CHARACTERISTICS. Although now only a fragment of the original castle, what survives is of particular significance because of the high quality and fine level of finish of the architectural detailing.
CONTEXTUAL CHARACTERISTICS. The surviving tower of Asloun castle, considered together with what survives and what can be ascertained of the rest of the building, shows it to have been a fine example of a particular approach to the design of houses with the residual trappings of defensibility. In this approach, a main block containing the principal and more 'public' rooms at first-floor level above domestic offices, is flanked by towers at diagonally opposite corners to create a Z-shaped plan. While this arrangement may have had some advantages in making provision for enfilading fire in case of attack, the main advantages were probably aesthetic (in creating an attractive grouping of masses) and domestic (in permitting differentiation of scale between 'public' and 'private' rooms, with easy horizontal access between the two). Such castles of Z-plan type form a small grouping that was particularly favoured in the north-east of Scotland
ASSOCIATIVE CHARACTERISTICS. The castle has some historic significance as probably being the place where the duke of Montrose stayed before the battle of Alford in 1645.
NATIONAL IMPORTANCE. The monument is of national importance for its potential to enhance our understanding of the domestic planning required by a middle-ranking lairdly family in north-eastern Scotland in the later sixteenth century. It derives additional significance from the archaeological potential of the surrounding area, where the main body and associated courtyards of the castle would have been located, as well as from the continuity of occupation of the site, which resulted in a portion of the tower being retained as a landscape focus within the grounds of the later residence.