The United Nations cultural organisation on Sunday added many of Iran's caravanserais, roadside rest stops for travellers along the country's ancient trade routes, to its World Heritage List.

The decision to register the 56 caravanserais, just a small percentage of the structures built in Iran, was made in Riyadh during the 45th session of the World Heritage Committee.

Caravanserais provided "shelter, food and water for caravans, pilgrims and other travellers," UNESCO said its website.

Iran boasts more than 200 caravanserais on historic trade routes that traverse the country linking Asia and Europe, including the Silk Road.

"They are considered to be the most influential and valuable examples of the caravanserais of Iran, revealing a wide range of architectural styles, adaptation to climatic conditions, and construction materials, spread across thousands of kilometres and built over many centuries," said UNESCO.

Among them are the caravanserais of Qasr-e Bahram near the city of Semnan, Deyr-e Gachin near Qom, and Anjireh Sangi near Yazd.

Iran now has 27 UNESCO-listed historical sites, including the ancient city of Persepolis, the capital of the Achaemenid Empire, Armenian monasteries in the northwest and the historic city of Yazd itself.