n the 1200s, when Marco Polo worked for Kublai Khan, the ruler of Mongolia and China, he was able to travel along the major roadways of the Khan's empire because he had the Khan's 'p'ai-tzu,' or official tablet of authority. These were made of wood, copper, or gold. The one issued to Marco Polo was of gold. This illustration shows Marco Polo's father and uncle, who had gone on an earlier trip to China and met the Khan, receiving a p'ai-tzu from the Khan. The illustration dates to about 1872.