Former US President Bill Clinton visited the City Wall in 1998.[Photo/ifeng.com]

3．Xi'an's City Wall

Xi'an's City Wall is one of the oldest and best preserved city walls in China and also one of the largest ancient military defense systems in the world.

Construction of Xi'an's first city wall began in 194 BC and lasted four years. The existing wall was started during the Ming Dynasty in 1370 and encircles 14 square kilometers of the city.

The City Wall has 18 gates, which are open for tourists to ascend the wall. No matter which gate you choose to enter, you can tour the whole circle of the wall.

In 1998, Bill Clinton, the former US president, climbed the City Wall from the South Gate with his family, and enjoyed the beautiful night scene. In 2014, US first lady Michelle Obama and her daughters viewed the City Wall and played shuttlecock with the help of local students.