The Fourth Rome(1996)
(The second book in the ARC Riders series)
A novel by David Drake and Janet Morris
A Soviet scientific team, left to its own devices after the collapse of the USSR, proceed with advanced experiments in time travel. Their objective is to delay the fall of the Roman Empire by 1,000 years--so that Rome's successor will be a Russian superpower that will rule the world. In order to preserve the present as we know it, the Arc Riders have to stop these renegade Soviets not only in present-day Russia, but in ancient Rome as well.
July 1996 : USA Mass Market Paperback
September 2009 : USA, Canada Kindle edition