American free climber Dean Potter walks on a 41-meter-long and two-centimeter-wide slackline over Enshi Grand Canyon at an altitude of 1,800m on April 22, 2012 in Enshi, Hubei Province of China. Potter successfully finished the lone slackline walk in about three minutes without taking any protective measures. (Photo by ChinaFotoPress/ChinaFotoPress)

Two ancient bronze coins, which according to Israel Antiquities Authority archaeologists were struck by the Roman procurator of Judea, Valerius Gratus, in the year 17/18 CE and recently were revealed in excavations beneath the Western Wall in Jerusalem's Old City are exposed to the media' on November 23, 2011 in Israel. (Photo by Lior Mizrahi/Getty Images)

The Eiffel Tour-the body language of balance. I came across this group of young adults from Sarajevo, Bosnia, having fun testing their balance two nights ago in on the Esplanade de Trocadero. (Photo and comment by Peter Turnley)

Measuring just five feet at its widest point, the ultra-thin home was unveiled in the Polish capital of Warsaw on Sunday, October 21, 2012. Photo: The Keret House is squeezed into the space between two apartment buildings in Warsaw. There's a four-inch gap between the apartment buildings to either side. A perforated steel facade was used to allow in more light. (Photo by Andrea Meichsner/The New York Times)

Emergency responders respond to the scene of a 565-foot-tall crane that toppled and flipped upside down, stretching along nearly two city blocks in downtown Manhattan in New York, February 5, 2016. The massive construction crane collapsed in lower Manhattan during a swirling snowstorm on Friday, killing one person and crushing a line of parked cars in the first accident of its kind in New York City since 2008. (Photo by Brendan McDermid/Reuters)

Expedition 44 flight engineer and NASA astronaut Scott Kelly seen inside the Cupola, a special module which provides a 360-degree viewing of the Earth and the International Space Station. Kelly is one of two crew members spending an entire year in space. (Photo by Scott Kelly/NASA)

A U.S. army soldier exercises in front of a M270A1 multiple launch rocket system as they prepare for a live-fire training exercise of the 6-37th Field Artillery Regiment at a training area near the demilitarized zone separating the two Koreas, in Cheorwon, South Korea, March 9, 2016. (Photo by Kim Hong-Ji/Reuters)

In this April 4, 2014 file photo, a community policeman kicks a man who they alledge participated in an ambush against them near the town of La Concepcion, Mexico. The vigilante force was set-up by affected communities opposed to the construction of the La Parota hydroelectric dam. Two vigilantes were injured and one died. (Photo by Bernandino Hernandez/AP Photo)