Creation by Gore Vidal
Before anything else, make sure to read the 2002 edition and not the original 1981. The author restored several chapters that the editor of the first version had cut and, in my opinion, are among the best.
Creation is an epic historical novel noted for its ambitious scope and erudition. It indulges in, even feasts on, skepticism towards established historical accounts and provides an unusual critical view of Classical Athens from a Persian perspective.
The novel is set in the 5th century BCE and its story follows Cyrus Spitama, a fictional Persian diplomat and grandson of Zoroaster, as he travels across ancient civilizations. Influential figures like Buddha and Confucius (and to a lesser extent Socrates) are weaved throughout the narrative, forcing a meeting of the religious and philosophical ideas of the time.
Vidal's depiction of Queen Atossa, the mother of Xerxes, is remarkable. She is portrayed as a powerful and influential figure in the Persian court, a cunning and ambitious woman who carefully plots to ensure her son Xerxes inherits the Persian empire. The vivid and memorable portrayal of Atossa’s significant role in the political intrigues within the Persian harem is often described as being equal to or greater than the King in power. Her influence extends beyond her son's ascension to the throne, contributing to the novel's exploration of power dynamics in the ancient Persian court.