a galloping horse leaving only dust behind it, on seeing this, the imperial comcubine smiles.
No one knows it was fresh lychee coming.
The background of story is the bold text in next paragraph
In the 1st century, fresh lychees were in such demand at the Imperial Court that a special courier service with fast horses would bring the fresh fruit from Guangdong. There was great demand for lychee in the Song Dynasty (960-1279), according to Ts'ai Hsiang, in his Li chi pu (Treatise on Lychees). It was also the favourite fruit of http://en.wikipedia.org/wiki/Emperor_of_China http://en.wikipedia.org/wiki/Emperor_Xuanzong_of_Tang_China's favoured concubine http://en.wikipedia.org/wiki/Yang_Guifei. The emperor had the fruit delivered at great expense to the capital.Another translated version of story list in the following text. It may help you understand what the sentence wans to convey.Viewed from Chang’an, Mount Li seemed a piece of embroidery;
Countless gates opened one after another on a hill-top.
At a horse raising red dust the imperial concubine smiled;
No one knew it was for the litchi fruit it had brought.
Please tell me if my sentence is understandable. If it's not too much trouble, also please help me to improve it.Thank you!