Story: Stranded in ancient Rome?

There was a series of three books that I read years ago, about a boy
who falls through a hole in time or something and gets stranded in
ancient Rome (or it might have been alternate-history Rome that
persisted until the present day). He triggers some sort of political
revolution in Rome, and then eventually goes to the New World, meets a
bunch of Aztecs, and winds up in the far East and meets an old Chinese
mystic who turns out to be either Roger Bacon or Francis Bacon. With
the sketchy details I remember, I haven't been able to locate the
books or the author. Does anyone know what I'm talking about?

-Max