Dirt roads and paths have been around for almost forever. If enough people traverse the same path often enough, it turns into a dirt road. The first known intentional roads (stone paved) date to about 4000 BC in Ur and Babylon. The next significant development in road construction was the Roman road system. A major part of how the Romans were able to build such an expansive road system was the durable concrete they used between stones. For years, researchers were unable to replicate the incredibly long-lasting Roman concrete despite having and following the recipe. It turned out the Romans used seawater.