The Silk Road was a main contributor to cultural diffusion when the Han Dynasty began. Ideas of government and religion spread from China to the Mediterranean Sea. During the time of the Han Dynasty silk compromised a large portion of trade from place to place. Years later the road it traveled was named the Silk road. Camels were the main source for transport, the road was long, harsh and very dry. Even though the Silk Road was nearly 4,000 miles long sickness spread quickly from place to place along it. Without some sort of weapon; merchants who traveled the road were often robbed and killed. The Silk Road gained much popularity when Marco Polo traveled along it in 1269 AD. Scattered near the silk road were ancient buildings and castles.