"Chang 'an" is another name for the imperial court. ("Cloud" and "Sun" use metonymy to refer to traitors and kings respectively. )
The green hills on both sides of the strait are opposite, and the solitary sails come from the sun. -Li Bai's Looking at Tianmen Mountain
Borrow some sails from the ship.
Why don't men take Wu Gou and accept fifty states in Guanshan? -Li He's South Garden.
"Wu Gou" borrowed weapons and "took Wu Gou" to join the army.