And concrete.

As i see it, Romans mainly gave us idea of "rule-based society" on which entire Western world stands. Even as Romans themselves made a joke out of it in their later history. But the idea was so transformative that even subsequent barbarian kings that ravaged Roman Empire after it's downfall, did not seek to formally overthrow it - rather, they pretended (with varying levels of plausibility) to lawfully inherit and rule it, or parts of it.