The Crown acquired the castle in the mid-fifteenth century. Its later defensive appearance owes much to a programme begun under James V in the 1530s and continued into the early 1540s. James Hamilton of Finnart directed important work, but neither his involvement nor the king's reign lasted for the whole programme. The building should not be described as the product of one uninterrupted medieval campaign.
Thickened curtain walls and large gun openings show how Blackness adapted to artillery. A low gun-gallery, known as a caponier, protected the approach before later alteration of the entrance defences. Such details make the castle more than a picturesque silhouette: they reveal deliberate attempts to control an attacker’s movement. The central tower and landward range also accommodated people, so defensive strength remained tied to the practical organisation of the place.
The prison brought Blackness into national religious and political disputes. Cardinal David Beaton was held here in 1543. Later prisoners included opponents of the religious settlement after the Restoration, and the central tower was altered in the 1660s for confinement. Prison conditions varied with status and circumstances; it would be misleading to imagine that every prisoner occupied the same dungeon or experienced identical treatment.
During the civil war of Mary's reign, the garrison supported Mary, Queen of Scots. That allegiance is not evidence that she herself was imprisoned here. A later siege ended with the castle's surrender to Cromwellian forces in 1651. Some HES visitor material gives 1650, but its detailed Statement of Significance and the Cromwell Association's historical gazetteer support 1651. The discrepancy should be acknowledged rather than silently repeated as a certainty.
Blackness remained a military site after the Union of 1707. In 1870 it became Scotland's central ammunition depot, a transformation that brought new buildings and a pier as well as changes within the old enclosure. The War Office transferred it to the Office of Works in 1912, returned during the First World War, and finally left in 1919. Military use therefore continued long after its medieval defensive role had changed.
Restoration in the 1920s removed many recent army alterations, including a roof over part of the courtyard, and reconstructed upper portions of the towers. The present appearance is consequently not an untouched survival of the sixteenth century. Much archaeological evidence was also disturbed by clearance, but pockets of deposits may remain. The castle is protected as scheduled monument SM90036; its former separate Category A listing has been removed.
Walk around the exterior before examining the interior, using the water, the towers and the entrance to orient yourself. Then compare the heavy artillery work with the spaces adapted for residence, confinement and storage. Check the official visitor information for current access. Blackness rewards a measured visit because its compact footprint holds several different histories: royal authority, imprisonment, military supply and the later decision to present a restored fortress to the public.