Pax by Tom Holland

"Their warriors rather than standing and fighting as legionaries did, like men, would instead wheel and wheel again on fast-galloping horses, firing arrows over their shoulders as they sped away. All more disgraceful, then, that twice the Parthians should have routed a Roman invasion force. The first, launched in the final decade of the free republic, had been annihilated outside a city called Carrhae. Crassus, its commander, had lost thirty thousand men, seven eagles, and his own head. Two decades later, when Mark Anthony led a second attempt to subdue the Parthians, he had managed to survive the ensuing debacle with his head still on his shoulders - but again lost thirty thousand men. Augustus, preferring diplomacy to war, had negotiated the return of Crassus' lost eagles and an enduring peace... All these factors, to a man of Trajan's fearless cast of mind, were bound to furnish matter for thought." - Pax: War and Peace in Rome's Golden Age

The above from Pax by Tom Holland. A very enjoyable book that detail the famous Roman Pax that lasted surprisingly much less time than may generally be thought. Times in Rome had always been tumultuous though much so during the Pax. Enjoyed the book and would recommend it.