Anouilh's interpretation of the historical story, though often ironic, is more straightforward than T. S. Eliot's play on the same subject, Murder in the Cathedral, which was intended as primarily a religious treatment. However, there are one or two similarities in the interpretation.
In the Introduction to the play, Anouilh explained that he based it on a chapter of an old book he had bought because its green binding looked good on his shelves. He and his wife read the 30 pages about Thomas Becket, and she urged him to write a play about Thomas, so he did -- knocking out the first part in only 15 days. It was not until he showed the finished play to a friend that he found out the old book he had based it on was totally wrong about the facts. Having built his play on Becket's being a Saxon (when he was actually a Norman whose family was from near Rouen and called "Bequet" in French), Anouilh could not recast the play to accord with historical facts, so he decided to let it stand. Historical content that can safely be considered true are the conflicts between England and France, church and state, and the general portrayal of Becket's history.