LONDON — What did the Statute of Rhuddlan in 1284 lay the basis for? Who or what is Vindolanda? Where is the National Horseracing Museum? Name two habits that may start a fight with your neighbor in Britain.

These and other rather esoteric questions are what Meghan Markle, the American actress recently engaged to Prince Harry, Queen Elizabeth II’s grandson and the fifth in line to the throne, will have to master in order to become a British citizen.

Most Britons, even a prime minister, find them almost impossible to answer.

Ms. Markle, who was raised in Los Angeles, plans to seek British citizenship after she marries Prince Harry, Kensington Palace confirmed. It is a lengthy process that culminates in a torturous citizenship test that costs about $65 and is typically flunked by one-third to half of the applicants.