It’s one of the new Seven Wonders of the World. It held 50,000 excited spectators and smaller groups of less-enthusiastic participants, and fueled the resurgence of strong Roman rule.

So it’s no surprise that the Colosseum earns its place as one of the most impressive construction projects in history. But building the Colosseum was no easy task — what did it really take to birth this behemoth? We’re digging deeper to discover the impact and outcome of engineering an empire.

Roma Resurgens

Politics — not practicality — drove the construction of the Colosseum. After years of civil war, city-destroying fires and disastrous rulers such as Nero, emperor Vespasian of the Flavian dynasty decided it was time to restore Rome’s former glory. As noted by the Ancient History Encyclopedia, Vespasian minted coins with the inscription “Roma resurgens” — Rome rises again. He then set his sights on Nero’s former Golden House in the heart of Rome for his new engineering effort.

For Vespasian, the Colosseum represented stability: In the war-torn year after Nero’s suicide, four emperors claimed the throne. Vespasian was the last, ruling for 10 years and laying the foundation for the Flavian dynasty, which according to History.com “attempted to tone down the excesses of the Roman court, restore Senate authority and promote public welfare.” In approximately 72 A.D. he ordered the construction of the Colosseum; eight years later, his son Titus opened the gates and dedicated the amphitheater to the people of Rome.

Numerical Superiority

In the history of engineering, Roman projects often stand out for their focus on over-engineering — it’s why many of their aqueducts and amphitheaters have endured for millennia. Building the Colosseum was no exception; as noted by BBC History, drains were built 26 feet below the structure to carry away underground stream water. The doughnut-shaped foundation was made of concrete 39-42 feet deep around the outer walls and seating, and 13 feet deep under the arena’s inner ellipse. In addition, earth from the massive foundation hole was used to raise ground level around the Colosseum by 23 feet, allowing it to stand astride the skyline rather than shrink below.

Colosseum construction conformed to period-specific design sensibilities, which stated that ideal building scale was 5:3. This Roman ratio informed the length and width of the arena. Originally planned at 300 x 180 Roman feet, the arena was eventually adjusted to 280 x 168 — smaller but still in line with ratio requirements, reports BBC History. Eighty entrances let spectators into the building, with 45,000 seats and 5,000 spaces for standing-room only, according to the Ancient History Encyclopedia.

Let the Games Begin

The Colosseum was largely finished just eight years after being commissioned by emperor Vespasian, but he didn’t live to see opening night — his son Titus declared a festival to celebrate with 100 days of games including a mock naval battle. Full completion of the Colosseum happened under Titus’ successor Domitian, who built a two-level basement — known as the hypogeum — and added the velarium, a large awning that could be pulled over the arena to shade spectators. Also exciting (and terrifying)? Thirty-six trap doors to let animals loose in the arena or send unwitting gladiators tumbling into the hypogeum.

While history has forgotten the name of the architect(s) who designed this incredible structure, there’s no doubt about the amount of labor required. Building the Colosseum took over 100,000 slaves working for a decade. As the BBC points out, while the exterior of the Colosseum fairly shone with glimmering travertine, the structure is “really a triumph of brick-vaulting and cement.” Barrel vaults and radial walls helped distribute the massive downward force of the three-story building and allowed Roman builders to create soaring spans and arches that wouldn’t be possible without massive cement foundations and — as noted above — the penchant for Roman over-engineering.

Got a Permit for That?

Construction of the Colosseum was almost impossibly fast, owing largely to the use of slave labor. Without the need for workplace protection, city permits or weekend breaks, building this behemoth was relatively straightforward. Modern technology — such as backhoes, bulldozers and dump trucks — would probably put current construction times on par with Roman imperial builders. The bigger challenge? Standing the test of time. As noted by Science Alert, Roman concrete outstrips the strength and longevity of its modern counterpart. Where current concrete erodes in contact with seawater, Roman rock flourishes. While our cement crumbles over time, ancient aggregate grows stronger.

Cost is also a concern. Estimates put the budget of creating a Colosseum 2.0 at anywhere from $435 to $675 million — barring resource shortages, earthquakes or labor strikes. Put simply? We’d spend more for a structure that likely wouldn’t live up to historic potential.

Legends Never Die

Even standouts in the history of engineering don’t live forever. While Rome did enjoy a resurgence during the Flavian dynasty, multiple earthquakes and changing Roman tastes saw the building fall into disrepair by 600 A.D. By the 20th century, almost two-thirds of the original structure had been destroyed by a combination of neglect and material repurposing. In the 1990s, restoration efforts began and while the Colosseum still falls short of its former glory, it remains one of Rome’s most popular attractions.

The Colosseum remains a tangible testament to engineering will and wonder — despite its troubled past, there’s no denying its place in the grand history of engineering.