Factual error: In the mini-series, Marco and Chinkin visit the Great Wall of China. Apart from the fact that the real Marco Polo probably never visited the Wall - he doesn't mention it in his writings - the Wall shown is Ming Dynasty. This version of the Wall was constructed in the 16th and 17th century, more than 300 years after Marco Polo's death.
Factual error: When Marco and Phags-pa are having a conversation near the end of the mini-series, you can see that the scene is set at the Summer Palace near Beijing. This is a mistake, as the Summer Palace was constructed in the 18th century under the Qing Dynasty, some 450 years after Marco Polo's death.