New Slains Castle, to distinguish it from nearby Old Slains Castle, was originally a 16th-century tower house, built by the 9th Earl of Erroll. The wings around the courtyard were extended in 1664 by addition of a gallery or corridor, and in 1707 the entrance front was renewed.
In the 1830s the 18th Earl commissioned the Aberdeen architect John Smith to remodel the castle. This resulted in a virtual rebuilding of Slains in a Scots Baronial style, including granite facings, in 1836–1837. Gardens were laid out in the late 1890s.
At first inspection the ruin appears to be a blend of several different architectural styles and periods, due to diverse masonry including older mortared granite, mortared medieval red brick, mortared sandstone and newer well faced granite. In fact most of the architecture seems to derive from a rather cohesive interval 1597 to 1664, which construction is the most expansive and includes the mortared rough granite and medieval brick. The 1836 work adds smoother granite facing that contrasts with the older construction style.
The defensive works of the castle include use of the North Sea cliffs; an abyss to the west that functions as a deep impassable moat; and a ruined rampart that would have been the main entrance on the south. The ruins include reasonably well preserved elements of three- and four-storey structural elements and a basement course over some of the range, especially at the eastern side. There are well-preserved basement kitchen works with numerous firepits and masonry indented storage spaces. The internal doorways are primarily of well-preserved wooden lintel construction, with numerous examples of mortared sandstone and medieval brickwork archways. The interior of the ground level is a maze of passageways and smaller rooms, reflecting a high state of occupancy in 17th-century times.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.