(CNN) — It's said if you don't visit the Terra-cotta Army while in Xi'an, your visit to the ancient Chinese city doesn't count.
Constructed more than 2,200 years ago, the army of warrior statues has since guarded the tomb of the emperor Qin Shi Huang, the first ruler to unify China, from 221-207 BC.
Thousands of years later, the soldiers are still there, witnessing the rapidly changing world in solemn silence.
Discovered by chance in 1974 by local farmers digging a well, the Terra-cotta Army is now described by some as the Eighth Wonder of the World.
Millions visit the site each year, including world leaders and dignitaries, which is located in Lintong, 25 miles from the Xi'an city center.
The entire area benefits from tourism, which generated 4.6 billion yuan ($720 million) in 2014, according to the local government.
Greatness and cruelty
Since the discovery of the warriors, archaeologists have excavated three pits, uncovering more than 8,000 life-size Terra-cotta figures, horses and chariots.
Experts believe the figures reveal the emperor's craving for eternal greatness.
Amazingly, no two figures are exactly alike.
Each warrior has unique facial features.
Details were so painstakingly sculpted by ancient craftsmen that even hairlines can be clearly identified.
Infantry, archers, generals, cavalry ... the military hierarchy is distinguished by the weaponry each figure holds and positions in which they stand.
Du Wenyiyu, a historian at Shaanxi Normal University, tells CNN the warriors showcase an extraordinary level of craftsmanship and artistry in play 2,200 years ago.
"Look at the soldiers and horses, they were just so vividly carved," he says with the enthusiasm of a first-time visitor.
Terra-cotta concubines and musicians, too
Du, who first saw the warriors when the site was under excavation in 1974, says the grand army reveals a strong burial tradition -- in ancient China, people believed souls carried on in another world.
"The emperor had the strongest army in the world when he was alive, so he wanted the same strong army after he died," says Du.
But it's not just soldiers.
Terra-cotta musicians, officials and concubines have been found in other pits.
"He wanted exactly the same grand services and treatment for his afterlife," says Du.
Before Qin Shi Huang, emperors would bury people alive.
Du believes creating terra-cotta figures to replace people as funerary objects represents a significant move forward in civilization.
More than 700,000 craftsmen worked round the clock for about two decades to build Qin Shi Huang's mausoleum.
Known for his cruelty, the emperor later killed the laborers who were overly familiar with the map and layout of the underground palace.
Upon excavation, few of the warriors or horses were fully intact.
The now-famed figures lining the pits have all been restored by experts over the past 40 years.
Hundreds of experts are still restoring the warriors by putting together broken pottery pieces.
It takes about a month to reconstruct a single clay warrior.
When the warriors were created, they were painted in bright colors.
Sadly, much of the color vanished almost immediately after excavation.
Even modern digging and preservation techniques are of little help.
The army is only part of a garrison in Qin Shi Huang's mausoleum, which covers nearly 14,000 acres -- a little bigger than the size of Vatican City.
Most of it remains unearthed.
More than 400 additional pits have been discovered near the Terra-cotta Army, but the massive underground palace largely remains mystery, as scientists are afraid of damage that might be caused by hurried evacuation efforts.
Bus: Bus 306, 914 and 915 run to the museum from the main train station just outside the North Gate (not the fast train station, further north). These are frequent routes with the route labeled in English on the side of the bus.
Taxis cost about 120 yuan ($19) for a one-way trip from Xi'an.
Hired cars (you can arrange through hotel desk) run about 400 yuan ($62.50) for a day trip, including the time the driver waits for your party.