Mr. Vidal clearly enjoys discovering illustrious men in unlikely postures, and never more than in this novel. ''No other man alive has traveled in as many lands as I,'' Spitama says. He has been a friend to kings, philosophers, emperors, generals and sages; a school chum of Xerxes, employer of Socrates (''I hired him to repair the front wall of the house''), and has sat at the feet of both the Buddha and Confucius. To put it mildly, Spitama is like the ultimate performer in that old Skippy Peanut Butter television show ''You Are There.'' He is even as breezy and priggish as the historical narrators who figured on that program...

As a novel of ideas, its ambition and its cast of characters could not possibly be bolder, but I for one would have found the going easier if I had been admitted to anything like plain vulgar domesticity. Banquets, perorations and sanctimonious chat cannot entirely displace one's craving for so much of what Mr. Vidal, speaking through Spitama, has ignored: a sense of place and the uneven texture of common humanity. ''The journey from Lu to Magadha over the silk road took nearly one year. Much of the time, I was ill ... I no longer remember, in any detail, the exact route that we took. ...'' This sort of elision is fairly frequent in the novel, and I tend to think that if Spitama had remembered the more ordinary and perhaps more sensual occurences that lay between his meetings with the sages of the century, it would have been a far richer novel - a great one, instead of a good one that all too often fails to avoid the sort of patrician name-dropping that mars so many historical epics.