From Imperial Twilight: The Opium War and the End of China’s Last Golden Age, by Stephen R. Platt (Knopf, 2018), Kindle pp. 49-50:
Qianlong was enthroned in 1735 at the age of twenty-four and would rule longer than any Chinese emperor ever had, or ever would again. He presided over massive frontier wars in Central Asia and sponsored cultural projects of a scale unimaginable in the West. (At a time when there were more book titles in China than in the rest of the world combined, he oversaw the compilation of a literary encyclopedia that ran to more than thirty-six thousand volumes in length and would fill a large room.) He was an accomplished and prolific classical poet and a renowned practitioner of calligraphy, and with a firm hand for government and a taste for over-the-top displays of power and beneficence he guided the empire to its apex of prosperity.
The first Qing rulers had begun the work of carving out their empire’s borders after the conquest of Beijing from the Ming dynasty in 1644. Over generations they expanded westward into Central Asia, beyond the original heartland of the fallen Ming, assimilating new territories in the southwest and the island of Taiwan to the east. But it was not until Qianlong’s reign in the eighteenth century that the Qing Empire reached its fullest flower, largely setting the boundaries for the Chinese state that exists today. At its peak under Qianlong, the empire reached all the way from Manchuria in the northeast to the provinces of Guangxi and Yunnan in the southwest, and from Taiwan off the eastern coast deep into Central Asia with the territories of Xinjiang and Tibet in the far west. It was an empire of four and a half million square miles, larger than all of Europe put together.
When Macartney came to pay his respects, Qianlong was just turning eighty-two. He was a sturdy man with drooping eyes, slight jowls, and a long mustache. His reign had been long enough that he was the same ruler who sat on the throne at the time of James Flint, the same who had originally ordered British trade confined to Canton. By the time of the Macartney embassy, Qianlong had ruled China for nearly fifty-eight years. He was not alone in his longevity either, for his grandfather Kangxi had reigned for sixty-one years, from 1661 to 1722, the two of them forming the backbone of one of the most powerful dynasties in China’s long history.