There is a small exhibition just to the right of the entrance of the British Museum devoted to its Bakor Monolith, bought from an auction house in 1974, having previously been owned by Mr. C.A.L. Brooks (so far, untraced) (https://www.britishmuseum.org/exhibitions/bakor-monoliths-endangered-heritage):-
These monoliths were first documented by Charles Partridge, a British colonial officer in 1903, who took photographs of them shown in the exhibition:-
They were then studied in the 1960s by Philip Alison, who worked for the Nigerian Forestry Department. He documented 295 stones. Many were smuggled out to Cameroon during the Biafran War.
If you want to know more, there is an accompanying book, currently only available under the counter:-
And an interview in Cultural Property News (https://culturalpropertynews.org/interview-factum-foundations-ferdinand-saumarez-smith/).