One of the ancient highways that has been connecting the continents, is the Silk Road that extends from east China to the middle Europe.
The Silk Road was used by caravans for more than 1600 years, yet it did not have a specific name up to 100 years ago. Although, some historians attribute its naming history to Marco Polo, Actually it was by the German scholar, Ferdinand von Richthofen that this cultural path was named and recognized as "The Silk Road". However, trade on this road was not limited to silk, other products such as Spices from India was also trade from this Road hence the name "Spice Road" was popular as well.

The Part of "the Silk Road" in Iran, was extended from Tous , and Nishapur to Ray , which continues to Qazvin then there will be two Roads, one goes through Soltaniyeh and Zanjan reaches Erzurum in Turkey and goes through the Black Sea to Istanbul .

The other branch of the Silk Road is the same western highway that runs from Hamadan to Baghdad.
The Silk Road not only was a way for the caravans to pass but also cultures, customs and techniques, including writing, knitting, agricultural techniques, and horseback6 riding were also moved the same route from East to West. The technology of making paper spreads through the Silk Road to other states. In some sources the Silk Road protraction is about eight thousand kilometers. It was not possible to travel all this route with limited Facilities, so the Caravansaries were built on this road, and equipment such as lanterns and minarets became the cultural legacy of traveling on this road.