How did the litchi eaten by Yang Guifei in the Tang Dynasty get to Chang 'an?

In the late Tang Dynasty, Du Mu wrote a poem "Three Poems Passing the Huaqing Palace One", in which he wrote, "Looking back at Chang 'an, there are piles of embroiderers, and the top of the mountain opens a thousand times. As soon as I rode on the smile of smoke and smoke, no one knew that the fresh fruit litchi was sent from the south. "This poem tells that the emperor ordered people to send lychees to Yang Guifei for thousands of miles, which vividly exposed the arrogance and extravagance of the rulers, and did not hesitate to select the people and waste money. So litchi is a very delicate fruit. How did it get to Chang 'an?

Litchi, also known as Danli, belongs to Sapindaceae. It tastes sweet and nutritious, and can quench thirst and soothe the nerves. It has always been loved by the public, and many poets have created many immortal poems for it. Litchi grows in warm areas and needs more humidity and sufficient light to ensure the sweetness of its fruit. It is a subtropical evergreen fruit tree with a growth temperature of about 24 ~ 29℃, which can't tolerate low temperature. Litchi in China is generally distributed in Fujian and coastal areas of Guangdong and Guangxi.

But in the Tang Dynasty, I didn't want modern transportation and logistics to be so developed. I wanted to eat lychee and fly for two or three days. At that time, the carriage was the main means of transportation, but litchi could only be kept fresh for 3 ~ 5 days at the earliest. Besides, it was sent to Chang 'an from Fujian, Guangdong and Guangxi thousands of miles away. So how did litchi get to Chang 'an?

There is no clear record in the history books, but it is not difficult to see from this ancient poem that before sending boxes of lychees to his beloved princess, Emperor Xuanzong of the Tang Dynasty ordered people to find the best horses, travel day and night, and constantly change riders. But how difficult the process is, we don't know and can't verify it, but we can probably imagine that the rulers are chilling the people at all costs for their own selfish desires.