Tupopdan Peak, 20,033 feet (6,106 meters), also known as "Passu Cathedral," just north of Gulmit village in the Hunza Valley region of Pakistan, photographed on July 28, 2015. The picturesque valley was one of several important passes along the ancient Silk Road, situated between China's western Xinjiang region and Afghanistan's Wakhan Corridor. #

Towers of ancient city walls in Xi'an, China, photographed on June 18, 2016. Xi'an (formerly known as Chang’an, and once an imperial capital city) was the eastern departure point for the Silk Road—a hub for traders in China's central Shaanxi Province. These city walls were largely built after the Silk Road had fallen into disuse, after 1500 A.D. #

Travelers heading west from Xi'an would first pass through Gansu Province. Here, a sandstorm hits the town of Shandan in Zhangye, Gansu Province, China, on March 5, 2013. #

In 1958, the Chinese government built the Jiuquan Satellite Launch Center in a remote area of Gansu province, near part of the old Silk Road. Here, the Shenzhou-9 spacecraft and its carrier rocket are being moved to the launch platform on June 9, 2012. #

Part of the Great Wall of China, built during the Ming Dynasty in Jiayuguan City, Gansu Province, photographed on July 4, 2013. Although the paths and roads here were used for centuries, these fortifications were built after the boom times of the Silk Road. #

A solar eclipse, called 'Rishi,' meaning 'eaten sun' in Chinese, can be seen above visitors at the Jiayuguan Fort on the Great Wall of China in the town of Jiayuguan, Gansu Province, on August 1, 2008. #

A model poses on a catwalk in the desert of Singing Sand Dunes on the outskirts of Dunhuang in Gansu Province. She walks for French fashion designer Pierre Cardin, on October 20, 2007. The oasis of Crescent Moon Spring in the Gobi Desert is now a tourist destination, but was once an important stopping place for Silk Road travelers. #

Caves in the Flaming Mountains valley, photographed on September 17, 2015, in Tuyoq Valley in Turpan, Xinjiang Uighur Autonomous Region, China. The area is dotted with grottoes and caverns that served many purposes over the centuries. They were used as rest stops, Buddhist temples, and even small villages. #

A view of the ruins of the ancient city of Jiaohe, seen at sunset on March 7, 2007 in Turpan, China. Jiaohe, built on a 98-foot-high loess plateau over 2,300 years ago, lies in the Yarnaz Valley and is protected by the natural fortification of the precipitous cliffs. The city has been a major passageway for communication between the East and West since the Han Dynasty and Tang Dynasty, and an important section of the ancient Silk Road. #

Urumqi, the capital city of Xinjiang Uighur Autonomous Region, China, photographed on June 9, 2008. Once largely a nomadic region, the city began about 1,300 years ago as a local seat of government, collecting taxes on caravans passing Silk Road. Today it is a modern city with a population of about 3.5 million. #

Flag-festooned poles stand over a grave in a cemetery surrounding the tomb of Imam Asim in the Taklamakan Desert outside the village of Jiya near Hotan, Xinjiang, China, on March 21, 2017. #

The old town of Kashgar, in the far western Xinjiang province, China, on June 27, 2017. Kashgar has long been considered the cultural heart of Xinjiang for the province's nearly 10 million Muslim Uighurs. At an historic crossroads linking China to Asia, the Middle East, and Europe, the city has changed under Chinese rule with government development, unofficial Han Chinese settlement to the western province, and restrictions imposed by the Communist Party. Beijing says it regards Kashgar's development as an improvement to the local economy, but many Uighurs consider it a threat that is eroding their language, traditions, and cultural identity. The friction has fueled a separatist movement that has sometimes turned violent, triggering a crackdown on what China's government considers 'terrorist acts' by religious extremists. #

A northern branch of the Silk Road would have taken travelers through southern Kazakhstan. Here, a farmer's yurt, or traditional nomad felt tent, is seen in front of a Soviet-era observatory on the mountainous Assy Plateau, about 2,500 meters (8,202 feet) above sea level, 56 miles (90 km) east of Almaty, Kazakhstan, on August 1, 2013. #

A tourist stands at the edge of the Singing Sand Dunes. Here, a large 495 foot (150 meter) dune which is famous for the noises it produces, in Altyn-Emel National Park in Kazakhstan's Almaty region, on May 12, 2016. #

An Afghan man rides a horse overlooking Band-e-Amir Lake, in the first national park in Afghanistan in the central province of Bamiyan, on November 5, 2016. Bamiyan stands in a deep green and lush valley stretching 100 kilometers through central Afghanistan, on the former Silk Road. #

Afghan girls look at the town of Bamiyan from the Shahr-e Gholghola ruins during a visit on August 7, 2017. Shahr-e Gholghola, the "City of Screams," was a fortified city captured by Genghis Khan in the 13th century. #

This photo taken on June 7, 2015, shows the projected image of a Buddha statue that had been destroyed by the Taliban in 2001 in Bamiyan. The initiative to visually restore the destroyed antiquities was dreamed up by Chinese couple Zhang Xinyu and Liang Hong, who are traveling through countries on the historic Silk Road Road. #

Afghan children play in the old part of the northern town of Mazar-i-Sharif in Balkh province on March 27, 2012. Once known as the "mother of cities," the ancient city of Balkh was a popular destination along the ancient Silk Road. Balkh was destroyed by Mongol conqueror Genghis Khan during his rule, and the city's ruins remain a tourist attraction today. #

An Afghan worker collects a silkworm cocoon from dried mulberry leaves in Zandajan district of Herat province, Afghanistan, on May 22, 2014. Once a stop along the Silk Road, western Afghanistan has a long tradition of producing silk used to weave carpets, a process that dates back thousands of years. Carpets are Afghanistan's best-known export, woven mostly by women and children in the north of the country, a trade which once employed, directly or indirectly, six million people, although that figure has since dropped sharply. In cooperation with a non-profit organization, the Department of Agriculture in Herat provided some 5,050 silkworm boxes to several districts at the beginning of 2014 to revive silk production in the region. 42,500 women and their families were involved in the project, which aimed to provide a means of subsistence and potentially lead to international market access for silk producers in the country. #

A father teaches his son to ride a horse in a pasture of the Suu-Samyr Plateau in Kyrgyzstan, 2,500 meters above sea level, along the ancient Silk Road from Bishkek to Osh, some 200 kilometers from Bishkek, on August 7, 2013. #

A view of Osh, the second-largest city in Kyrgyzstan, seen from nearby Sulayman Mountain, on March 26, 2016. Osh was once a major marketplace along the Silk Road, and was considered the midpoint on the route. #

Merv, Turkmenistan, was once a great oasis city that thrived along the Silk Road. The Great Kyz Kala, photographed here on September 16, 2011, is one of several large ruined fortress-like buildings that are all that remain of Merv today. #

In modern Iran, the golden dome of the mausoleum of Imam Reza stands in Mashhad, 500 miles (800 kilometers) east of Tehran, on August 11, 2008. Mashhad was the most prominent city along the Silk Road corridor out out Afghanistan and Turkmenistan. #

Homes in the village of Kandovan, Iran, photographed on June 26, 2007. Kandovan is a village where homes are dug out of the rock formations in the foothills of Sahand Mountain. Residents claim that the village dates back to the time of the Mongol hordes, when their ancestors made their homes here, seeking safety. #

A southern branch of the Silk Road took travelers through Yazd, Iran, home to a large community of Zoroastrians. The Towers of Silence were used by early Zoroastrians as a site for a sky burial tradition. Photographed near Yazd on January 29, 2009. #

The old citadel of Arg-e Bam in Kerman province, Bam, Iran, on January 2, 2016. This Silk Road citadel stood at an oasis and a crossroads, serving as a place of rest, a market, and a point of defense. #

A family rides a motorcycle past the Amir Chakhmaq Hosseinieh worship site, one of the largest of such structures in Iran, on June 1, 2014, in the desert town of Yazd. #

In Iraq, a man visits the Taq Kasra, or the Archway of Ctesiphon, a Persian ruin on the Tigris River near Salman Pak, south of Baghdad, on July 18, 2012. Ctesiphon was once an ancient city on the Tigris and a hub on the Silk Road, connecting to many other routes throughout the region. Today, the arch is one of the few remaining structures left after the rapid fall of Ctesiphon about 1,300 years ago. #

A view of the mausoleum of prophet Daniel, who is supposedly buried here, in Kirkuk, Iraq. Located between Mosul and Bagdad, Kirkuk has been a prosperous city on the ancient Silk Road and one of the biggest oil-producing centers of the region. #

Part of the ancient Syrian city of Palmyra, after government troops recaptured the UNESCO world heritage site from ISIS jihadists on March 27, 2016. Palmyra was an ancient caravan city, its wealth and fortunes strongly linked to the steady flow of Silk Road travelers coming and going. #

Daily life around the outer walls of the citadel in the center of the old city of Aleppo, Syria, on January 06, 2011. The Citadel of Aleppo is a large medieval fortified palace which is considered to be one of the oldest and largest castles in the world. Usage of the citadel hill dates back at least to the middle of the 3rd millennium B.C. Aleppo is also one of the oldest continuously inhabited cities in the world; it has been inhabited since perhaps as early as the 6th millennium B.C. The city was a strategic trading point midway between the Mediterranean Sea and Mesopotamia. The city's significance in history has been its location at the end of the Silk Road, which passed through central Asia and Mesopotamia. #

Ancient columns stand at the Al-Mina archaeological site, South Governorate, Tyre, Lebanon, on May 3, 2017. Tyre, on the Mediterranean Sea, served as one of several ports at the western end of the Silk Road. Traders, having reached this point, might unload their goods onto a waiting ship, or board the vessel themselves to continue westward—or, turn around and head back toward Xi'an once again, more than 4,000 miles away, as the crow flies. #