Throughout history, walls have been constructed as part of nations’ and kingdoms’ defensive structures to keep barbarian hordes, marauding rebels, and recalcitrant tribes out of defined geographic areas. Defensive walls were usually constructed by fairly advanced and sophisticated peoples, such as the Romans and Chinese, with varying degrees of success. Of course, the most famous of all defensive walls in the world is the Great Wall of China, which is actually a series of walls and forts built over the span of several centuries. The Chinese built the Great Wall of China, and several others, primarily to keep invaders from the north, such as the Mongols, out of their land, or at least to slow them down as they fled north after raids. The Romans also built spectacular walls, most notably the Antonine Wall and Hadrian’s Wall. The purpose of those walls was to set the northern limit of the Roman Empire at approximately the modern border of England and Scotland, and, like the Great Wall of China, it was intended to keep out or slow down marauding barbarian tribes from the north. The Great Wall of China is perhaps the wonder of the world that has most captured the human imagination, and as the quotes about it indicate, the wall has acquired special significance even outside of China. The places and ways in which it has taken hold vary greatly, but one thing is certain: the Great Wall of China is as amazing as it is mysterious, and it’s as mundane as it is magical. Naturally, the Great Wall has become the most recognizable symbol of China, used for both aggrandizement and criticism. Nationalists see it as a symbol of China's peaceful nature, engineering capability, and historic longevity, while detractors see the Great Wall as the embodiment of China's backwardness, closed-mindedness, and hubris. Though the wall can symbolize all of these things about China, it is important to remember that the many long walls. upon some of which the current landmark was constructed, were put up by specific people for specific purposes. The Romans were master builders, and much of what they built has stood the test of time. Throughout their vast empire they have left grand structures, from the Forum and Pantheon in Rome to the theatres and hippodromes of North Africa and the triumphal gates in Anatolia and France. Wherever they went, the Romans built imposing structures to show their power and ability, and one of their most impressive constructions was built on the northernmost fringe of the empire. Shortly after the emperor Hadrian came to power in the early 2nd century A.D., he decided to seal off Scotland from Roman Britain with an ambitious wall stretching from sea to sea. To accomplish this, the wall had to be built from the mouth of the River Tyne – where Newcastle stands today – 80 Roman miles (76 miles or 122 kilometers) west to Bowness-on-Solway. The sheer scale of the job still impresses people today, and Hadrian’s Wall has the advantage of being systematically studied and partially restored. A study of the wall and its history provide an insight not only into the political context of Rome at the time but the empire’s incredible engineering capabilities. The Sasanians built an equally impressive wall in central Asia, one that was longer than Hadrian’s Wall and by all accounts just as effective when it was still in use. Throughout the centuries, the Sasanian wall has gone by several different names, but it is now known as the “Great Wall of Gorgan” due to its length and location near the city of Gorgan in the modern nation-state of Iran. The Great Wall of Gorgan was used much longer than the better known Roman walls to keep enemies at bay. From the 5th century A.D., and possibly centuries earlier, the Great Wall of Gorgan continually served as a military wall and fortification system until sometime after the Arab Muslim conquest of central Asia in the mid-7th century A.D.