Today’s infrastructure investment can help drive economic growth for millennia — look no further than the Roman Empire’s legacy in Europe: A group of Danish economists have put forth a theory that infrastructural investment is one of the main drivers of economic growth and development, which could explain why contemporary Europe is as prosperous and developed as it is, Christopher Ingraham writes for the Washington Post. “They demonstrate that the density of ancient Roman roads at a given point in Europe strongly correlates with present-day prosperity, as measured by modern-day road density, population density and even satellite imagery of nighttime lighting.” According to the economists, the massive road network built by the Roman Empire laid the groundwork for prosperity by creating trade routes and allowing for greater levels of economic activity today.

The Romans built roads in North Africa, too, but they were not maintained as well as Europe’s: The MENA region apparently turned its back on wheeled transport sometime between the 5th and 10th centuries, meaning Roman roads “weren’t maintained the same way they were in Europe, where cart-based transit remained dominant. ‘The implication of these developments is that since ancient roads fall into disrepair in the MENA region, to a much greater extent than in Europe, one should expect to see much less persistence in infrastructure density.”