It would have dramatically altered the Edinburgh skyline as we know it - but the plans never got off the ground.
This new digitally-rendered image shows how Edinburgh Castle might have looked today had one particular set of designs been approved.
It is based on 1862 sketches and designs by architect David Bryce for a a Memorial Keep in honour of Prince Albert, who died the year before.
But Queen Victoria, Albert’s widow, disapproved of the construction, and the tower was never erected.
The image is part of a series of digital renderings based on some of the UK’s most surprising unbuilt structures, created for a project called Unbuilt Britain: What 6 cities could have looked like.
Researchers trawled the archives for forgotten plans and schematics to help bring these structures to life.
Other cities involved in the project include Bristol, London, Liverpool, Manchester and Newcastle.
There have been few changes to Edinburgh Castle’s outline since the 18th century, but more than one proposal has emerged for new features.
For example, following World War I, Frank Charles Mears suggested a Scottish National War Memorial route lined with monuments.
Mr Mears envisaged a “Sacred Way” which would have seen a series of new monuments and memorials created in the shadow of the castle to honour those who fell the First World War.
Join our Facebook group Our Edinburgh to share images and news from and around the Capital