The First Man in Rome marked a stylistic departure for McCullough, as well as a new genre to explore. It is the first of a series of novels, something new for McCullough. Also new is that the primary characters are male. Finally, as a historical novel rather than a romance with a historical setting, it adheres to historical fact. Of necessity, a historical novelist knows the large events of a story before beginning to write. The historical novelist’s only literary freedom lies in details such as personality and domestic life. Such details are McCullough’s chief strength.

Gaius Marius is the primary character of The First Man in Rome. He is an aristocrat from the far provinces, a man of wealth but little social standing in a society that values ancestry highly. Through marriage to a daughter of the Caesar family and a brilliant military career, he obtains prestige and fame, becoming in time the first man in Rome. This is the accepted title for a man whose natural attributes allow him to outshine all others.

More than in any other work, except perhaps The Thorn Birds, McCullough uses setting as a major character in the novel. The aristocrats of her Rome devote themselves to their country. They are expected to be politicians and military generals, and they are reared with a sense of duty to value Rome above all. The women also are bounded by well-defined and rigid rules of duty to home and family. Their adherence to these rules allows the men to concentrate on politics and war.

The novel is dense with detail. Included in the book are several maps, a glossary, a pronunciation guide for Latin names and phrases, and a list of characters. In the narrative, the buildings, streets, clothes, and attitudes are depicted with minute accuracy. While this makes for slow reading, the narrative constructs a fully rounded, embracing picture of Rome that allows the reader to sense just how the state could so encompass the lives of its inhabitants. It also allows McCullough to reconstruct the ancient world for a modern reader.

As a result of the limits of historical accuracy, the characters in this book are not subjected to the same extremes of fortune that the characters in McCullough’s other novels are. Disasters do occur; battles are won or lost; a lucky thought promotes a person to fame and an unlucky chance causes death. The causes, however, are inherent in the individuals, or are likely chances. Working within a story that has already been lived allows McCullough to concentrate fully on her characters and reduces the number of coincidences moving the plot along.