One soldier to rule them all

Third scenario, Rome. Two guys and one elephant landed. There is no intelligence at all with my guys so they just stand there and let them walk right by and destroy everything. So when I finally noticed, this is exactly what happened:
two guys and one elephant destroy a dozen archers, 6 horse dudes, almost instantly, with 5 towers firing at them, one of their soldiers remained. That single soldier then after he killed my guys, destroyed all 5 towers, every guy i made who spawned which was another 6 guys, then that single guy killed all my villagers and then all my buildings. One single guy.