It seems there might be a bit of confusion in your statement regarding the Great Wall and trade. The Great Wall of China was primarily constructed for defense against invasions and incursions from nomadic tribes to the north. While the wall itself was not directly associated with trade, it played a role in the protection of trade routes, including the Silk Road.
The Silk Road was indeed vital for trade during the Han dynasty, where goods such as silk were exchanged with other cultures, promoting economic and cultural exchanges.
So, if we adjust your statement for clarity, it would read:
"One of the most lasting contributions to China by the Han dynasty was the establishment of trade routes, particularly the Silk Road, through which the Chinese traded silk and received various goods and cultural influences."