Aquiliad Series by S.P. Somtow, Somtow Sucharitkul

On this alternate Earth, Rome rules all . . . including the New World, known in other dimensions as America but here as Terra Novo. General Titus Papinianus is governor of that untamed land, and Aquila, chief of the savage Lacoti nation, is a Roman senator. But official titles aside, their duty is to Caesar. So when Caesar sends them on a quest for the fabled land of China, thought to be somewhere in Terra Novo, off they go... moreOn this alternate Earth, Rome rules all . . . including the New World, known in other dimensions as America but here as Terra Novo. General Titus Papinianus is governor of that untamed land, and Aquila, chief of the savage Lacoti nation, is a Roman senator. But official titles aside, their duty is to Caesar. So when Caesar sends them on a quest for the fabled land of China, thought to be somewhere in Terra Novo, off they go. They are hardly prepared for bloodthirsty Aztecs, flying machines, time-traveling aliens, or Bigfoot—and Aquila's problem-solving strategies are unconventional to say the least! Before they know it, their adventures lead them into the hands of the Time Criminal, who is bent on altering all the multiple universes to suit his own evil whims. Somehow they have to stop him . . . before their world is destroyed! less

Equus Insanus, son of the intrepid Aquila, finds the civilized life of Rome tedious. So he is eager to return to his native land of Terra Novo to assist in the construction of Caesar's latest fancy—a transprovincial railroad.But on this alternate Earth where the Roman Empire rules America, things seldom go as planned... moreEquus Insanus, son of the intrepid Aquila, finds the civilized life of Rome tedious. So he is eager to return to his native land of Terra Novo to assist in the construction of Caesar's latest fancy—a transprovincial railroad.But on this alternate Earth where the Roman Empire rules America, things seldom go as planned. Soon the project is beset with savage Indian raids and inexplicable disasters…and Equus's father returns from the future with a dire warning: The evil Time Criminal is back and stronger than ever, and even Aquila of the time-trading Dimensional Patrol is powerless to act!Now only Equus Insanus stands between the Time Criminal and the destruction of the universe! less

Equus Insanus, son of Aquila, has been missing for three years on his quest to bring the vile Time Criminal to justice. His Roman half brother, Lucius, nephew to Caesar, fears him dead—until he begins receiving strange messages from the lost Lacoti warrior. Then Lucius learns that Equus has been captured by the Time Criminal, who plans to use him as the instrument which will destroy their world... moreEquus Insanus, son of Aquila, has been missing for three years on his quest to bring the vile Time Criminal to justice. His Roman half brother, Lucius, nephew to Caesar, fears him dead—until he begins receiving strange messages from the lost Lacoti warrior. Then Lucius learns that Equus has been captured by the Time Criminal, who plans to use him as the instrument which will destroy their world. Discovering that the secret to Equus’s salvation may lie in the pyramids of Giza and in the riddle of the Sphynx, Aquila and Lucius set out for Egypt. They have no idea that the answers they find will lead them across the entire Roman Empire, through space, and ultimately through time itself—for the final confrontation with the Time Criminal and the battle for a man’s soul! less