Nick Brown 
Black Stone [EPUB ebook] 
Agent of Rome 4

AD 273. Obsessed by the solar religions of the east, the emperor Aurelian sets out to obtain every sacred object within his realm. But one — a mysterious rock said to channel the power of the sun god — lies beyond his reach. Warrior-priest Ilaha has captured the legendary stone and is using it to raise an army against Rome.For Imperial agent Cassius Corbulo and ex-gladiator bodyguard Indavara, stopping him constitutes their greatest challenge yet. Assisted by a squad of undercover soldiers and a Saracen chieftain, they trek south across the deserts of Arabia, encountering sandstorms, murderous money-lenders and a ruthless German mercenary. And when they finally reach Ilaha’s mountain fortress, they face thousands of warriors who will give their lives to protect him … and the black stone.