Other significant British novelists include Georgette Heyer, Naomi Mitchison and Mary Renault. Heyer essentially established the historical romance genre and its subgenre Regency romance, which was inspired by Jane Austen. To ensure accuracy, Heyer collected reference works and kept detailed notes on all aspects of Regency life. While some critics thought the novels were too detailed, others considered the level of detail to be Heyer's greatest asset; Heyer even recreated William the Conqueror's crossing into England for her novel "The Conqueror". Naomi Mitchison's finest novel, "The Corn King and the Spring Queen" (1931), is regarded by some as the best historical novel of the 20th century. Mary Renault is best known for her historical novels set in Ancient Greece. In addition to fictional portrayals of Theseus, Socrates, Plato, Simonides of Ceos and Alexander the Great, she wrote a non-fiction biography of Alexander. "The Siege of Krishnapur" (1973) by J. G. Farrell has been described as an "outstanding novel". Inspired by events such as the sieges of Cawnpore and Lucknow, the book details the siege of a fictional Indian town, Krishnapur, during the Indian Rebellion of 1857 from the perspective of the town's British residents. The main characters find themselves subject to the increasing strictures and deprivation of the siege, and the absurdity of maintaining the British class system in a town no one can leave becomes a source of comic invention, though the text is serious in intent and tone.