Question: In what year were the Manchus able to cross the Great Wall?
About the article "Great Wall of China", section "Ming era".

Candidate passages:
The Great Wall concept was revived again during the Ming Dynasty in the 14th century, and following the Ming army's defeat by the Oirats in the Battle of Tumu.
The Ming had failed to gain a clear upper hand over the Manchurian and Mongolian tribes after successive battles, and the long-drawn conflict was taking a toll on the empire.
The Ming adopted a new strategy to keep the nomadic tribes out by constructing walls along the northern border of China.
Acknowledging the Mongol control established in the Ordos Desert, the wall followed the desert's southern edge instead of incorporating the bend of the Yellow River.
Unlike the earlier fortifications, the Ming construction was stronger and more elaborate due to the use of bricks and stone instead of rammed earth.
Up to 25,000 watchtowers are estimated to have been constructed on the wall.
As Mongol raids continued periodically over the years, the Ming devoted considerable resources to repair and reinforce the walls.
Sections near the Ming capital of Beijing were especially strong.
Qi Jiguang between 1567 and 1570 also repaired and reinforced the wall, faced sections of the ram-earth wall with bricks and constructed 1,200 watchtowers from Shanhaiguan Pass to Changping to warn of approaching Mongol raiders.
During the 1440s–1460s, the Ming also built a so-called "Liaodong Wall".
Similar in function to the Great Wall (whose extension, in a sense, it was), but more basic in construction, the Liaodong Wall enclosed the agricultural heartland of the Liaodong province, protecting it against potential incursions by Jurched-Mongol Oriyanghan from the northwest and the Jianzhou Jurchens from the north.
While stones and tiles were used in some parts of the Liaodong Wall, most of it was in fact simply an earth dike with moats on both sides.
Towards the end of the Ming Dynasty, the Great Wall helped defend the empire against the Manchu invasions that began around 1600.
Even after the loss of all of Liaodong, the Ming army held the heavily fortified Shanhaiguan pass, preventing the Manchus from conquering the Chinese heartland.
The Manchus were finally able to cross the Great Wall in 1644, after Beijing had already fallen to Li Zicheng's rebels.
Before this time, the Manchus had crossed the Great Wall multiple times to raid, but this time it was for conquest.
The gates at Shanhaiguan were opened by the commanding Ming general Wu Sangui on May 25 who formed an alliance with the Manchus, hoping to use the Manchus to expel the rebels from Beijing.
The Manchus quickly seized Beijing, and defeated both the rebel-founded Shun Dynasty and the remaining Ming resistance, establishing the Qing Dynasty rule over all of China.
Under Qing rule, China's borders extended beyond the walls and Mongolia was annexed into the empire, so constructions on the Great Wall were discontinued.
On the other hand, the so-called Willow Palisade, following a line similar to that of the Ming Liaodong Wall, was constructed by the Qing rulers in Manchuria.
Its purpose, however, was not defense but rather migration control.
The fall of the Ming Dynasty was a protracted affair, its roots beginning as early as 1600 with the emergence of the Manchu under Nurhaci.
Under the brilliant commander, Yuan Chonghuan, the Ming was able to repeatedly fight off the Manchus, notably in 1626 at Ning-yuan and in 1628.
On May 26, 1644, Beijing fell to a rebel army led by Li Zicheng.
Seizing their chance, the Manchus crossed the Great Wall after Ming border general Wu Sangui opened the gates at Shanhai Pass, and quickly overthrew Li's short-lived Shun Dynasty.
Despite the loss of Beijing and the death of the emperor, Ming power was by no means destroyed.
Nanjing, Fujian, Guangdong, Shanxi, and Yunnan were all strongholds of Ming resistance.
Each bastion of resistance was individually defeated by the Qing until 1662, when the last real hopes of a Ming revival died with the Yongli emperor, Zhu Youlang.
Complete pacification of China would not be complete until 1683. 
In 1628, under the new government, Yuan Chonghuan was reinstated as field marshal of all the forces of the Northeast.
He embarked on an ambitious five-year plan for the complete recovery of Liaodong.
The Chongzhen Emperor had begun his reign in 1627 at the age of 16, and in 1629 (at the age of 18) he appointed Yuan Chonghuan.
In 1629 Yuan was granted the title of "Senior Guardian of the Heir Apparent".
The Chongzhen Emperor gave him his Imperial Sword and stated that he would fully support Yuan's decisions.
This time Yuan had to face again a larger Manchu force of over 200,000 troops under Huang Taiji.
The Manchus had incorporated more men in their army, including the newly surrendered Mongols, Ming rebels, conquered Korea, and various small tribes of the North.
However, the Manchus were reluctant to attack Jinzhou or Ningyuan and never did so again.
The Manchus changed their strategy.
Bypassing Jinzhou, Ningyuan and Shanhai Pass, they broke through the Great Wall west of Shanhai Pass and reached north of Beijing in the winter of 1629.
Yuan rushed back with an elite army from Ningyuan to defend the capital.
He reached Beijing just days before the Manchus.
Outside the city wall of Beijing, he defeated the Manchurian "Eight Banners" which numbered around 100,000 men, but failed to destroy the Manchu army.
The Manchus' surprise attack on Beijing was foiled.
Despite the fact that Yuan prevented the Manchus from even reaching the city wall, Yuan was heavily criticized when he arrived in Beijing, and some eunuchs even accused Yuan of collaborating with the enemy.
In fact, they were actually tricked by Huang Taiji into thinking that Yuan had betrayed them.
The Chongzhen Emperor ordered Yuan's arrest during an audience with the Emperor on 13 January 1630.
Despite little evidence, he was accused of collusion with the enemy and condemned to death by "slow slicing" at Ganshiqiao () in Beijing.
When Yuan was asked for last words before his execution, he produced the poem: "A life's work always ends up in vain; half of my career seems to be in dreams.
I do not worry about lacking brave warriors after my death, for my loyal spirit will continue to guard Liaodong."
() Imperial records show he took half a day to die.
Yuan was mourned throughout most of the country outside Beijing and even in Joseon Korea.
After his death, many regarded the Ming and their allies as extremely vulnerable to Manchu invasion.
It was said that upon hearing of his apparent "betrayal", many Beijing residents hated him so much that they rushed to buy his body parts so they could eat them.
He was left there after the torture, shouting for half a day before stopping.
His head, the only recognizable part after the torture, was taken outside the Inner City Wall by a city guard, whose surname is She, and buried in Huashi near Guangqumen.
The guard's family have guarded it for generations since.
His tomb was recently renovated to become the Yuan Chonghuan Memorial.
Huang Taiji publicly stated that he would never be able to beat Yuan in a fair game, thus having the Chongzhen Emperor kill him was the only method to get rid of him.
Just as the message of Yuan's death reach Huang Taiji's ears, he changed his dynasty's name from Jin to Qing and proclaimed himself Emperor Qing Taizong.
Historical records state that Huang Taiji feared Yuan's last words that his soul would always guard Liaodong Peninsula.
Some say to overcome Yuan Chonghuan, whose name means "Undying Flames" (which contains the element of Fire), he had his dynasty name changed to Qing, meaning "to cleanse", which contains the Chinese element of "Water". 
The last decades of the Ming saw famines, floods, economic chaos, rebellions, and invasions.
In 1618, the upstart Jianzhou Jurchen leader Nurhaci united the tribes of Manchuria and declared war on the Ming.
After the Fushun garrison within the Liaodong Wall surrendered to Nurhaci the next year, the Ming court assembled a four-pronged Chinese–Korean army numbering above a 100,000 men to contain him, but they were catastrophically defeated at the Battle of Sarhu.
Nurhaci made substantial progress in his conquest of Liaodong until he was mortally wounded at the 1626 Battle of Ningyuan by Yuan Chonghuan.
He was succeeded by his son Hung Taiji, who worked to undermine Yuan Chonghuan by spreading rumours of Yuan's collaboration with the Jurchens.
To drive the point home, Hung Taiji sent an army around Ningyuan through Mongol territories to breach the Great Wall pass at Xifengkou in the fall of 1629, taking advantage of a rift in the Ming ranks due to Yuan Chonghuan's execution of his fellow commander Mao Wenlong.
This was the first time the Jurchens had broken through the Great Wall into China proper since the troubles in the northeast began.
Yuan Chonghuan hastily sent an army to drive off the raiders from the walls of Beijing, but political damage had already been done.
Yuan Chonghuan was accused of treason for letting this happen, and in 1630 he was executed by slow dismemberment while his family were exterminated or exiled.
Following Hung Taiji's raid, regular garrison troops in the western defence zones along the Great Wall were sent east to defend the capital, which had the unintended consequence of instigating more instability.
The regions of Shaanxi had already been afflicted by adverse weather, heavy taxation, and fiscal mismanagement, so the removal of a substantial military presence encouraged the inhabitants to turn to banditry and rebellion; the remaining garrison forces, already unpaid and resentful, saw little choice but to throw in their lot with the rebels.
A prominent leader who rose from the ranks of the rebels was Li Zicheng, the self-titled "Dashing Prince" (闖王, "Chuǎng Wáng") who came to dominate Central China by 1642.
Throughout his rise there were several occasions on which he could have been extinguished by the Ming, but Jurchen breaches of the Great Wall – the Jurchens had raided across the Great Wall several times since 1629, including in 1634, 1638, and 1642 – distracted the Ming court's attention.
The Ming were not able to effectively deal with the simultaneous internal and external threats, much less maintain a consistent defence along the Great Wall.
In 1635 Hung Taiji renamed his people the Manchus and declared himself the emperor of a new Qing dynasty the following year.
However, the Manchus were not yet willing to launch an invasion of conquest against the Ming; as Hung Taiji remarked in 1642, "The Shanhai Pass cannot be taken.
"In the first months of 1644, Li Zicheng, having consolidated control over his home province Shaanxi, declared himself the founder of a new Shun dynasty, and marched against the Ming court in Beijing.
His invasion route brought the Shun army along the Great Wall to neutralize its heavily fortified garrisons.
In this effort Li was met with next to no resistance as most garrisons surrendered to the Shun with no major fighting, except at the Ningwu Pass where the general Zhou Yuji (周遇吉) fought to the death.
By April17, both the major garrisons at Datong and Xuanfu had surrendered to Li Zicheng, and most Ming hopes were placed on the last Great Wall pass at Juyong and its defender Tang Tong ().
However, just as the Ming court was discussing the means of increasing provisions to Juyong Pass, it received word that Tang Tong had surrendered and let the Shun army through on April21.
With all options exhausted, the last Ming emperor Chongzhen hanged himself as the Shun army entered Beijing on April25, 1644.
The largest remaining Ming fighting force in North China at the time of Beijing's fall was Wu Sangui's 40,000-man frontier force, who had abandoned the Ningyuan garrison to come to the emperor's aid.
Halfway to Beijing, Wu received news of Chongzhen's death, so he went back to garrison the Shanhai Pass, the eastern terminus of the main Great Wall line.
He and his men were now caught between the rebels within the Great Wall and the Manchus without.
After some deliberation, Wu Sangui decided to resist the new Shun regime, having heard that Li Zicheng had ordered Wu's family executed.
On May3 and May10 Wu Sangui twice defeated the Shun vanguard led by the turncoat Tang Tong, but he knew that his force alone was insufficient to fight Li Zicheng's main army.
Wu Sangui wrote to the Manchus for help, promising "great profits" if they assisted him in defeating the rebels.
The Manchu prince-regent Dorgon (Hung Taiji had died in 1643) determined that this was the opportunity to claim the Mandate of Heaven for the Qing.
Dorgon made clear in his reply that the Manchus would help Wu Sangui, but Wu would have to submit to the Qing; Wu had little choice but to accept.
On May27, as the Shun army approached the Shanhai Pass from the south, Wu Sangui opened the gates to let the Qing army through the pass from the north.
Up to this point the Battle of Shanhai Pass between Li Zicheng and Wu Sangui had been moving in Li's favour, but the sudden appearance of the Manchu bannermen decisively routed the Shun forces.
Having thus entered through the Great Wall, the Manchus seized Beijing on June5.
They eventually defeated both the rebel-founded Shun dynasty and the remaining Ming resistance, establishing Qing rule over all of China.
Opinions about the Wall's role in the Ming dynasty's downfall is 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. 
Near the end of the 1500s, the extremely centralized government that gave so much power to the emperor had begun to fail as more incompetent rulers took the mantle.
Along with these weak rulers came increasingly corrupt officials who took advantage of the decline.
Once more the public projects fell into disrepair due to neglect by the bureaucracy and resulted in floods, drought, and famine that rocked the peasantry.
The famine soon became so terrible that some peasants resorted to selling their children to slavery to save them from starvation, or to eating bark, the feces of geese, or other people.
Many landlords abused the situation by building large estates where desperate farmers would work and be exploited.
In turn, many of these farmers resorted to flight, banditry, and open rebellion.
All of this corresponded with the usual dynastic decline of China seen before, as well as the growing foreign threats.
In the mid-16th century, Japanese and ethnic Chinese pirates began to raid the southern coast, and neither the bureaucracy nor the military were able to stop them.
The threat of the northern Manchu people also grew.
The Manchu nomads were an already large state north of China, when in the early 1600s a local leader named Nurhaci suddenly united them under the Eight Banners—armies that the opposing families were organized into.
The Manchus adopted many Chinese customs, specifically taking after their bureaucracy.
Nevertheless the Manchus still remained a Chinese vassal.
In 1644 Chinese administration became so weak, the 16th and last emperor, the Chongzhen Emperor, did not respond to the severity of an ensuing rebellion by local dissenters until the enemy had invaded the Forbidden City (his personal estate).
He soon hanged himself in the imperial gardens.
For a brief amount of time, the Shun Dynasty was claimed, until a loyalist Ming official called support from the Manchus to put down the new dynasty.
The Shun Dynasty ended within a year and the Manchu nomads were now within the Great Wall.
Taking advantage of the situation, the Manchus marched on the Chinese capital of Beijing.
Within two decades all of China belonged to the Manchu nomads and the Qing Dynasty was established.