BY Arbor House, $17.95. As though to prove that he can turn out as conventional a historical novel as any other writer, Mr. Burgess has done just that— although surely nobody can have seriously asked him to do it, or would have reproached him if he had not. The enterprise is mysterious, but the novel itself is a very efficient work of its kind. It begins with the Crucifixion and ends with the destruction of Pompeii, along the way deploying a horde of characters, covering a large territory, and steadily contrasting the vicissitudes of the early Christian community with the bloody depravities of the Roman imperial court. It is written with the learning, skill, and vitality characteristic of Mr. Burgess’s work. It puts no strain at all on the reader’s convictions or imagination, which is not characteristic of Mr. Burgess’s work and therefore leaves one wondering what he is doing in this galley..