If spacecraft OSIRIS-REx can grab a piece of an asteroid and bring it back to Earth, scientists could gain great insight into our planet's origins, and even how to defend against rogue asteroids. But NASA only gets three shots at collecting a sample.

If spacecraft OSIRIS-REx can grab a piece of an asteroid and bring it back to Earth, scientists could gain great insight into our planet's origins, and even how to defend against rogue asteroids. But NASA only gets three shots at collecting a sample.

As global temperatures rise, scientists are exploring geoengineering solutions, from planting trees to sucking carbon out of the air to physically blocking out sunlight. But would it work? And what are the risks of engineering Earth's climate?

As global temperatures rise, scientists are exploring geoengineering solutions, from planting trees to sucking carbon out of the air to physically blocking out sunlight. But would it work? And what are the risks of engineering Earth's climate?

The Colosseum is a monument to Roman imperial power and cruelty. Its graceful lines and harmonious proportions concealed a highly efficient design and advanced construction methods that made hundreds of arches out of 100,000 tons of stone. In its elliptical arena, tens of thousands of gladiators, slaves, prisoners and wild animals met their deaths. Ancient texts report lions and elephants emerging from beneath the floor, as if by magic, to ravage gladiators and people condemned to death. Then, just as quickly, the Colosseum could be flooded with so much water that ships could engage in sea battles. Could these legends be true? Now, with access to one of the world's most protected world heritage sites, archaeologists and engineers team up to re-create ancient Roman techniques to build a 25-foot lifting machine and trap-door system capable of releasing a wolf into the Colosseum's arena for the first time in 1,500 years.

The Colosseum is a monument to Roman imperial power and cruelty. Its graceful lines and harmonious proportions concealed a highly efficient design and advanced construction methods that made hundreds of arches out of 100,000 tons of stone. In its elliptical arena, tens of thousands of gladiators, slaves, prisoners and wild animals met their deaths. Ancient texts report lions and elephants emerging from beneath the floor, as if by magic, to ravage gladiators and people condemned to death. Then, just as quickly, the Colosseum could be flooded with so much water that ships could engage in sea battles. Could these legends be true? Now, with access to one of the world's most protected world heritage sites, archaeologists and engineers team up to re-create ancient Roman techniques to build a 25-foot lifting machine and trap-door system capable of releasing a wolf into the Colosseum's arena for the first time in 1,500 years.

More than two thousand years ago, the thriving city of Petra rose up in the bone-dry desert of what is now Jordan. An oasis of culture and abundance, the city was built by wealthy merchants whose camel caravans transported incense and spices across hundreds of miles from the Arabian Gulf. They carved spectacular temple-tombs into its soaring cliffs, raised a monumental Great Temple at its heart, and devised an ingenious system that channeled water to vineyards, bathhouses, fountains, and pools. But following a catastrophic earthquake and a slump in its desert trade routes, Petra's unique culture faded and was lost to most of the world for nearly a thousand years. Now, in a daring experiment, an archaeologist and sculptors team up to carve an iconic temple-tomb to find out how the ancient people of Petra built their city of stone.

As global temperatures rise, scientists are exploring geoengineering solutions, from planting trees to sucking carbon out of the air to physically blocking out sunlight. But would it work? And what are the risks of engineering Earth's climate?

As global temperatures rise, scientists are exploring geoengineering solutions, from planting trees to sucking carbon out of the air to physically blocking out sunlight. But would it work? And what are the risks of engineering Earth's climate?

The Colosseum is a monument to Roman imperial power and cruelty. Its graceful lines and harmonious proportions concealed a highly efficient design and advanced construction methods that made hundreds of arches out of 100,000 tons of stone. In its elliptical arena, tens of thousands of gladiators, slaves, prisoners and wild animals met their deaths. Ancient texts report lions and elephants emerging from beneath the floor, as if by magic, to ravage gladiators and people condemned to death. Then, just as quickly, the Colosseum could be flooded with so much water that ships could engage in sea battles. Could these legends be true? Now, with access to one of the world's most protected world heritage sites, archaeologists and engineers team up to re-create ancient Roman techniques to build a 25-foot lifting machine and trap-door system capable of releasing a wolf into the Colosseum's arena for the first time in 1,500 years.

The Colosseum is a monument to Roman imperial power and cruelty. Its graceful lines and harmonious proportions concealed a highly efficient design and advanced construction methods that made hundreds of arches out of 100,000 tons of stone. In its elliptical arena, tens of thousands of gladiators, slaves, prisoners and wild animals met their deaths. Ancient texts report lions and elephants emerging from beneath the floor, as if by magic, to ravage gladiators and people condemned to death. Then, just as quickly, the Colosseum could be flooded with so much water that ships could engage in sea battles. Could these legends be true? Now, with access to one of the world's most protected world heritage sites, archaeologists and engineers team up to re-create ancient Roman techniques to build a 25-foot lifting machine and trap-door system capable of releasing a wolf into the Colosseum's arena for the first time in 1,500 years.

More than two thousand years ago, the thriving city of Petra rose up in the bone-dry desert of what is now Jordan. An oasis of culture and abundance, the city was built by wealthy merchants whose camel caravans transported incense and spices across hundreds of miles from the Arabian Gulf. They carved spectacular temple-tombs into its soaring cliffs, raised a monumental Great Temple at its heart, and devised an ingenious system that channeled water to vineyards, bathhouses, fountains, and pools. But following a catastrophic earthquake and a slump in its desert trade routes, Petra's unique culture faded and was lost to most of the world for nearly a thousand years. Now, in a daring experiment, an archaeologist and sculptors team up to carve an iconic temple-tomb to find out how the ancient people of Petra built their city of stone.

More than two thousand years ago, the thriving city of Petra rose up in the bone-dry desert of what is now Jordan. An oasis of culture and abundance, the city was built by wealthy merchants whose camel caravans transported incense and spices across hundreds of miles from the Arabian Gulf. They carved spectacular temple-tombs into its soaring cliffs, raised a monumental Great Temple at its heart, and devised an ingenious system that channeled water to vineyards, bathhouses, fountains, and pools. But following a catastrophic earthquake and a slump in its desert trade routes, Petra's unique culture faded and was lost to most of the world for nearly a thousand years. Now, in a daring experiment, an archaeologist and sculptors team up to carve an iconic temple-tomb to find out how the ancient people of Petra built their city of stone.

Discover Campi Flegrei, a lesser-known volcano in the shadow of Vesuvius. If it erupts, millions of lives could be at risk. Meet the scientists exploring its geography and developing a warning system to prevent Naples from becoming the next Pompeii.

The Franklin Expedition is explored 160 years after vanishing while charting the Northwest Passage.

Istanbul's magnificent Hagia Sophia has survived on one of the world's most active seismic faults, which has inflicted a dozen devastating earthquakes since Hagia Sophia was built in 537 AD. As Istanbul braces for the next big quake, a team of architects and engineers is investigating Hagia Sophia's seismic secrets. NOVA follows the team's discoveries as they examine the building's unique structure and other ingenious design strategies that have insured the dome's survival. The engineers build a massive eight-ton model of the building's core structure, place it on a motorized shake table and hit it with a series of simulated quakes.

Istanbul's magnificent Hagia Sophia has survived on one of the world's most active seismic faults, which has inflicted a dozen devastating earthquakes since Hagia Sophia was built in 537 AD. As Istanbul braces for the next big quake, a team of architects and engineers is investigating Hagia Sophia's seismic secrets. NOVA follows the team's discoveries as they examine the building's unique structure and other ingenious design strategies that have insured the dome's survival. The engineers build a massive eight-ton model of the building's core structure, place it on a motorized shake table and hit it with a series of simulated quakes.

As global temperatures rise, scientists are exploring geoengineering solutions, from planting trees to sucking carbon out of the air to physically blocking out sunlight. But would it work? And what are the risks of engineering Earth's climate?

The Colosseum is a monument to Roman imperial power and cruelty. Its graceful lines and harmonious proportions concealed a highly efficient design and advanced construction methods that made hundreds of arches out of 100,000 tons of stone. In its elliptical arena, tens of thousands of gladiators, slaves, prisoners and wild animals met their deaths. Ancient texts report lions and elephants emerging from beneath the floor, as if by magic, to ravage gladiators and people condemned to death. Then, just as quickly, the Colosseum could be flooded with so much water that ships could engage in sea battles. Could these legends be true? Now, with access to one of the world's most protected world heritage sites, archaeologists and engineers team up to re-create ancient Roman techniques to build a 25-foot lifting machine and trap-door system capable of releasing a wolf into the Colosseum's arena for the first time in 1,500 years.

More than two thousand years ago, the thriving city of Petra rose up in the bone-dry desert of what is now Jordan. An oasis of culture and abundance, the city was built by wealthy merchants whose camel caravans transported incense and spices across hundreds of miles from the Arabian Gulf. They carved spectacular temple-tombs into its soaring cliffs, raised a monumental Great Temple at its heart, and devised an ingenious system that channeled water to vineyards, bathhouses, fountains, and pools. But following a catastrophic earthquake and a slump in its desert trade routes, Petra's unique culture faded and was lost to most of the world for nearly a thousand years. Now, in a daring experiment, an archaeologist and sculptors team up to carve an iconic temple-tomb to find out how the ancient people of Petra built their city of stone.

Istanbul's magnificent Hagia Sophia has survived on one of the world's most active seismic faults, which has inflicted a dozen devastating earthquakes since Hagia Sophia was built in 537 AD. As Istanbul braces for the next big quake, a team of architects and engineers is investigating Hagia Sophia's seismic secrets. NOVA follows the team's discoveries as they examine the building's unique structure and other ingenious design strategies that have insured the dome's survival. The engineers build a massive eight-ton model of the building's core structure, place it on a motorized shake table and hit it with a series of simulated quakes.