He got up to go, and added: “Then I shall see you in the City before you go back to … Castra Parvulorum, was it? What a jolly name!”

“Unfortunately it isn’t generally called that,” the Archdeacon said. “It’s called in directories and so on, and by the inhabitants, Fardles. By Grimm’s law.”

“Grimm’s law?” Mornington asked, astonished. “Wasn’t he the man who wrote the fairy tails for the parvuli? But why did he make a law about it? And why did anyone take any notice?”

“I understand it was something to do with Indo-European sounds,” the Archdeacon answered. “The Castra was dropped, and in parvulorum the p became f and the v became d. And Grimm discovered what had happened. But I try and keep the old name as well as I can. It’s not far from London. They say Caesar gave it the name because his soldiers caught a lot of British children there, and he sent them back to their own people.” (War in Heaven, p 24)