<P> In 1567 Qi Jiguang and Tan Lun, successful generals who fended off the coastal pirates, were reassigned to manage the Ji--Chang Defense Commands and step up the defences of the capital region . Under their ambitious and energetic management, 1200 brick watchtowers were built along the Great Wall from 1569 to 1571 . These included the first large - scale use of hollow watchtowers on the Wall: up until this point, most previous towers along the Great Wall had been solid, with a small hut on top for a sentry to take shelter from the elements and Mongol arrows; the Ji--Chang towers built from 1569 onwards were hollow brick structures, allowing soldiers interior space to live, store food and water, stockpile weapons, and take shelter from Mongol arrows . </P> <P> Altan Khan eventually made peace with China when it opened border cities for trade in 1571, alleviating the Mongol need to raid . This, coupled with Qi and Tan's efforts to secure the frontier, brought a period of relative peace along the border . However, minor raids still happened from time to time when the profits of plunder outweighed those of trade, prompting the Ming to close all gaps along the frontier around Beijing . Areas of difficult terrain once considered impassable were also walled off, leading to the well - known vistas of a stone - faced Great Wall snaking over dramatic landscapes that tourists still see today . </P> <P> Wall construction continued until the demise of the Ming dynasty in 1644 . In the decades that led to the fall of the Ming dynasty, the Ming court and the Great Wall itself had to deal with simultaneous internal rebellions and the Manchu invasions . In addition to their conquest of Liaodong, the Manchus had raided across the Great Wall for the first time in 1629, and again in 1634, 1638, and 1642 . Meanwhile, the rebels led by warlord Li Zicheng had been gathering strength . In the early months of 1644, Li Zicheng declared himself the founder of the Shun and marched towards the Ming capital from Shaanxi . His route roughly followed the line of the Great Wall, in order to neutralize its heavily fortified garrisons . The crucial defences of Datong, Xuanfu, and Juyong Pass all surrendered without a fight, and the Chongzhen Emperor hanged himself on 25 April as the Shun army entered Beijing . At this point, the largest remaining Ming fighting force in North China was in Shanhai Pass, where the Great Wall meets the Bohai Sea . Its defender Wu Sangui, wedged between the Shun army within and the Manchus without, decided to surrender to the Manchus and opened the gates for them . The Manchus, having thus entered through the Great Wall, defeated Li Zicheng at the Battle of Shanhai Pass and seized Beijing on June 5 . They eventually defeated both the rebel - founded Shun dynasty and the remaining Ming resistance, establishing their rule over all of China as the Qing dynasty . </P> <P> Opinions about the Wall's role in the Ming dynasty's downfall are mixed . Historians such as Arthur Waldron and Julia Lovell are critical of the whole wall - building exercise in light of its ultimate failure in protecting China; the former compared the Great Wall with the failed Maginot Line of the French in World War II . However, independent scholar David Spindler notes that the Wall, being only part of a complex foreign policy, received "disproportionate blame" because it was the most obvious relic of that policy . </P>

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