Weighing the future, a lock at a time: six years after taking control of the Panama Canal, Panamanians face new challenges to keep this vital waterway economically viable and to protect their livelihood.

• Author: Balaguer, Alejandro

A huge tower, a patchwork of hundreds of containers, is passing through the dense tropical forests outlying Panama City. Seen from the avenue that circles around Balboa Harbor in the middle of the capital, the image defies reason. The multicolor, rectangular tower appears to be moving by itself. An enormous building in motion. But that's just an illusion. The actual truth is obvious: a cargo boat is passing through the Panama Canal.

The scene has changed quite a bit from the one Vasco Nunez de Balboa saw in 1513 when he discovered the Pacific Ocean after having crossed through the fearsome jungles of the narrow Panamanian isthmus from the Caribbean. It was the first journey though the untamed territory between the two oceans, and it was an adventure of unimagined scope that would later lead Balboa's ambitious right-hand man, Francisco Pizarro, to conquer the largest empire of pre-Columbian America.

After the Spaniards defeated the Inca emperor, all the gold, jewels, and silver of South America came through Panama, transported by mule over the narrow waist of Central America to the forts of San Lorenzo and Portobelo and, finally, by boat to Spain. It was a journey full of sacrifices, one of malaria-ridden marshes, prowling pirates, and other dangers. The jungle exacted a toll in human lives.

Centuries would go by before men would decide to undertake what many have called one of the greatest works of human engineering ever: the construction of the Panama Canal.

Inspired by the successful construction of the Suez Canal, the French were the first to accept the challenge of building a canal in Panama. It wasn't an easy task. In fact, it was plagued with setbacks and hardships. For Ferdinand de Lesseps, the charismatic French diplomat in charge of the construction operation, building a sea-level canal through Panama was the project of a lifetime. In later years, it would also be the cause of his disgrace and ruin.

The climate, a hostile environment, torrential rains, and two lethal invisible enemies--yellow fever and malaria--all wreaked havoc on the laborers.

In 1880, after years of back-breaking excavations, financial problems, and adversities--not to mention the devastating tropical diseases that took hundreds of lives--Lessep's Compagnie Universelle du Canal Interoceanique de Panama lost the support of its investors and went bankrupt. Construction came to a halt.

In 1904, however, after signing an agreement with the Panamanian government the previous year, the United States bought the canal rights and properties front the French and took over the task very capably.

Unlike the French, the Americans didn't want a sea-level canal. Their engineers faced many other challenges, and their equally heroic task included excavation across the continental divide, the design and construction of a canal with a series of locks and the largest lock gates ever imagined, and the...