Starting with simple logs from fallen trees or a few stones strategically placed across a stream, bridges and humans have had a long history. Many are designed exclusively for people on foot or on bike; others are for use by cars, boats or trains. Some bridges connect continents; others are known more for their histories and the cultural interest they inspire.

"Few man-made structures combine the technical with the aesthetic in such an evocative way as bridges" wrote David J. Brown, a bridge historian and author of Bridges: Three Thousand Years of Defying Nature. With the help of Brown, and Judith Dupré, a structural historian and bridge expert, we've searched the globe for incredible specimens of architecture that span physical obstacles—better known as bridges.

Primitive suspension bridge techniques may have been known and used in India and China around 2000 B.C. and possibly even earlier. Some of the world's oldest bridges are still in use, like the Ponte Sant'Angelo in Rome, one of the eight stone bridges the Romans are known to have built over the Tiber between 200 B.C. and A.D. 260. The Romans did not invent the arch, but were the first to construct large masonry arch bridges to span much greater distances than the flat deck bridges built previously. Many engineering principles introduced by the Romans are still in use today.

Bridges continue to be celebrated as marvels of engineering, like the Jiaozhou Bay Bridge (also called the Qingdao Haiwan Bridge) opened earlier this year in China, the most recent in a series of record-breaking bridges in the country. Creating the world's longest bridge across water was no small feat. The 26.4-mile-long, six-lane bridge was reported to have used 450,000 tons of steel in its construction — enough for almost 65 Eiffel Towers — along with enough concrete to fill 3,800 Olympic-sized swimming pools. The structure was designed to withstand earthquakes, typhoons, and the impact of a 300,000-ton vessel.

Other bridges may have started as technological wonders, but today are most remembered for the icons they have become. Take the the Golden Gate Bridge, an instantly recognizable symbol of San Francisco, or the Brooklyn Bridge, spanning the East River to connect Manhattan and Brooklyn, completed in 1883. "At the time, it was the longest suspension bridge in the world, and also New York City's tallest structure," said Dupré, structural historian and author of Bridges: A History of the World's Most Famous and Important Spans. Today the Brooklyn Bridge is the quintessential American emblem, a source of inspiration for immigrants and poets alike.

Some bridges harbor little known but surprising facts. The George Washington Bridge, for example, which spans the Hudson from upper Manhattan to New Jersey, built during the Great Depression, was originally designed to include apartments within the framed structure.

"People are passionate about bridges. They join together what had once been separate," said Dupré.

Jiaozhou Bay Bridge, Qingdao-Huangdao, China

Jiaozhou Bay Bridge, Qingdao-Huangdao, China

The world's longest bridge across water is in China. Opened in June 2011, the 26.4 mile long Jiaozhou Bay Bridge (also called the Qingdao Haiwan Bridge) in northeastern Shandong Province, spans Jiaozhou Bay and links the port city of Qingdao to Huangdao Island. Official reports say the six-lane, T-shaped road bridge cost about $2.3 billion to build and will cut the travel time in half. Nearly 450,000 tons of steel was used in its construction along with 2.3 million cubic meters of concrete. Chinese officials said the bridge was designed to be strong enough to withstand a magnitude 8 earthquake, typhoons, or the impact of a 300,000-ton vessel. China is already home to seven of the world's 10 longest bridges, including the lengthiest – the 102 mile Danyang-Kunshan rail bridge near Shanghai, which runs over land and water.