The British government considered the repartition of Ireland in a radical step during the 1980s at the height of The Troubles.
The plan, released in 30-year-old British cabinet papers, would have divided Northern Ireland in half, giving the southern part back to the Republic.
However West Belfast, a nationalist enclave, would have been walled off to keep it from being attacked by Protestant extremists.
The plans reached the desk of Margaret Thatcher, according to reports. It was based on an academic paper by Dr. Paul Compton of Queens University and described as a radical way to end violence. The plan also mentioned establishing a "walled ghetto" in west Belfast.
His "most respected analysis" was discussed in a secret paper prepared by the Northern Ireland Office and sent to Margaret Thatcher, who underlined many parts of it suggesting she was deeply interested.
A more modest plan putting parts of Fermanagh, south Armagh and most of Derry city in the Republic was also proposed.
Officials discussed creating a Catholic ghetto "a wedge-shaped area in west Belfast" but said there would be "difficulties over the Belfast sector."
It adds: "Policing international boundaries across Belfast and any corridor between republican Belfast and the Border would be a formidable task."
The plan was ultimately rejected after Irish leader Garrett FitzGerald expressed strong objections.