The Centurio Immotalis half dozed in his saddle as they approached the bridge over the Danuvius River. He’d decided to push on and hit their fort instead of camping outside the empire’s borders for another night. Although the day’s march had been stiff, his men were in fine spirits as they approached the river that meant they were only a few more miles from their beds.

“Princeps Primus Centurio?” a young soldier asked.

“Boy, ...