A cargo ship headed toward the Pacific winds its way across Gatún Lake and the Panamanian peninsula.

George F. Mobley/National Geographic/Getty Images

When the con­quistador Vasco Núñez de Balboa summited a peak in the region Dariên, his eyes beheld a tantalizing sight. Behind him, the Atlantic Ocean that he had crossed from Spain; before him, the Pacific -- the two bodies of water separated by an impossibly narrow isthmus. However, Balboa was simply the first in a long line of outsiders to underestimate the difficulty of connecting the two oceans. It took more than 400 years from his 1513 discovery to create the canal that revolutionized world trade.

Today, more than 943,042 vessels have passed through the Panama Canal since its opening [source: Panama Canal Authority]. It acts as benchmark to the world's economic health -- bustling with freighters carrying grain, petroleum and coal during high times and slowing down when global markets lag. The canal shortened the trip between the East and West coasts of the United States by 8,000 nautical miles (15,000 km), allowing ships to avoid the dangerous, expensive trip around South America's Cape Horn [source: Britannica].

The canal also occupies a strange place in geopolitics. Until 1979, it was under the exclusive control of the United States. The U.S.-run Canal Zone slashed through the Republic of Panama just as the canal cut through the American continents. It also served as a symbol of injustice for many Panamanians. But after a 20-year period of joint agency between the U.S. and the Republic of Panama, complete control passed to Panama. Since then, the Panama Canal Authority (an agency responsible to the Panamanian government) has managed the canal and maintained the waterway's safety record and efficiency.

That's a fairly impressive feat considering the volume of the canal's traffic -- and the age of th­e canal itself. Ships are raised and lowered over the continental divide by a series of locks, which are built with two chambers to accommodate two-way traffic. It's a trade artery, operating almost beyond capacity, and it was built in challenging terrain.

So what did it take to rend two continents? And why did an estimated 22,000 people die in a failed attempt to make it happen? We'll find out.