Limes Germanicus refers to the ancient Roman frontier that marked the northern boundary of the Roman Empire in what is now Germany. This defensive system included a series of fortifications, watchtowers, and military roads designed to protect Roman territories from invasions by various tribes. It stretched approximately 550 kilometers along the Rhine River. The construction of the Limes began in the 1st century AD and continued for several centuries. It played a crucial role in controlling trade and movement between the Roman Empire and the Germanic tribes. Today, parts of the Limes are recognized as a UNESCO World Heritage Site, highlighting its historical significance.