1.) A Roman legion was in the middle of a campaign, and they had to cross a river. In order to do so, they had to build a bridge and they managed to do it in about a week. They crossed the bridge, conquered *whoever*, and then after they had the new province they went back across the bridge and pulled it up as they went, just to show how unstoppable they were. (I think this might have been during one of Julius Caesar's military campaigns in Germania but I'm not sure.)
2.) When archeologists excavated ruins (at Pompeii?), they discovered that the foundation bricks of certain buildings had been laid in a diamond pattern rather than the traditional "horizontal" pattern. No one could understand why, until they realized that the diamond pattern allowed for much greater stability during earthquakes since the energy was absorbed and/or dissipated by it.
Thanks in advance!