City of Petra

You've seen this before. It's the "treasury" of the ancient, rock-cut city of Petra.

But do you know what it actually is — or more interesting, what's inside?

It isn't what you might expect

Most people don't know the full extent of Petra. When rediscovered in 1812 in Jordan, it was first thought to be a large necropolis.

They'd actually stumbled across an entire, functioning city — where 30,000 people once lived...

You access Petra via a single, narrow gorge called the Siq. As you approach, you get a glimpse of a huge, Hellenistic facade...

It's known as Al-Khazneh ("the treasury") because of the treasure once thought to be stored inside.

All cut straight out of the cliffside, with no stone added to the original cliff wall — so not a single mistake could've been made by those carving it.

The architecture is clearly Greek in influence: Corinthian columns, pediments, a central tholos. And a mix of Greek and Egyptian sculptural decorations.

But Ancient Greeks didn't build this...

Continue along the road and there's a whole city of these multi-story, Hellenistic-style facades.

They were all hand-cut 2,000 years ago by a mysterious tribe called the Nabataeans...

Nobody knows where they came from (probably nomads from Arabia), but they'd settled here by the 4th century BC.

A lot of what they built are tombs, but there are also homes, temples, gardens — much now below ground and yet to be excavated.

This was evidently a majestic city at its peak. There's even a theater capable of seating thousands, also hewn directly into the mountain.

What's more, this was once a lush, green paradise...

What made civilization possible here was a huge system of waterways, cisterns, and terracotta pipes.

Nabataeans were masters of capturing and transporting water over precise gradients, turning a few inches of annual rainfall into year-round supply.

Why here, in such a remote region of Jordan?

Because Petra was at a mighty crossroads of ancient trade. Incense, spices, and cloth came through, and taxing it made the Nabataeans immensely wealthy.

Old tradition claims the Three Wise Men got their frankincense and myrrh here on the way to Bethlehem.

Petra is steeped in biblical significance: it's mentioned twice in the Old Testament, and tradition places Moses striking water from rock nearby on his travels.

Back to the treasury though: the big question is what is it, and what's inside?

Given the elaborate ornamentation of the exterior, you'll be a little underwhelmed at first...

This is what it looks like. A plain interior marked only by a few huge doorways that lead seemingly nowhere.

Presumably, whatever furnishings once here were wooden, and long since pillaged...

Nearby, the giant "Urn Tomb" is similarly bare-walled inside. But when you realize how much dense stone was excavated to shape it, and how precise the corners are, you wonder how they did it.

It's thought Al-Khazneh was the tomb of King Aretas IV, who ruled the Nabataeans from 9 BC to 40 AD.

Nobody is really sure — it's just one of the things we don't fully understand about Nabataeans...

We don't know much about the gods they worshipped, or why they performed sacrifice rituals high above the city. The Greek historian Strabo wrote:

"They worship the sun, building an altar on the top of the house, and pouring libations on it daily and burning frankincense."

After centuries of autonomous rule, Petra was captured by the Romans. It declined in importance, was struck by earthquakes, and left abandoned by the Middle Ages.

Only to be found again centuries later — and proclaimed one of the 7 Wonders of the World...

Even more surreal: visiting Petra by night...