The bridges of the Thailand-Burma Railway were a throwback to bridges along 19th century American railroad lines, which were made almost entirely of timber. While it may be surprising that wood has the strength to support thousands of pounds of rail cars and cargo traveling over steep mountain passes, it is really just a simple matter of good engineering. The Thai-Burmese railway bridges and their American counterparts were timber truss bridges. Trusses, invented in the 16th century by Renaissance Italian architect Andrea Palladio and first used to support the roofs of houses, come in many different designs. But all trusses have elements — diagonal beams and center posts and a bottom rail — that form a triangle, which allows the load of the bridge or roof to be distributed throughout the structure. (A pile of sticks can be strong if the construction is right, but the wood remains at the mercy of the elements. For that reason, most of the timber truss bridges built in the United States were covered, to protect the trusses. The Japanese, who likely had neither the resources nor the time, did not cover the bridges of the Thailand-Burma line).

The most famous of the bridges on the “Death Railway” spanned the Khwae Noi River — the River Kwai — in Kanchanaburi, a western province of Thailand bordering Myanmar (Burma). The first of these River Kwai bridges, completed in February 1943, was fashioned entirely out of wood. It was used to transport light trains and materials across the river to other railroad construction sites. A stronger steel-and-concrete bridge was completed in April 1943. The bridge operated until February 13, 1945, when Allied bombardiers used conventional heavy bombs to blow out two of the bridge’s central spans.

The Bridge on the River Kwai may be famous, but according to Bashar Altabba, a structural engineer, it was not remarkable — and neither was any other one bridge or track or rock cutting along the railway’s route. Altabba, who works for HTNB Engineering in Boston on the city’s landmark “Big Dig” project, served as technical consultant for SECRETS OF THE DEAD: “Bridge on the River Kwai.” He saw first-hand what is left of the railway and the terrain on which it was built. “Throughout history, engineers have done much bigger, much grander, much longer, on a one-time basis,” Altabba says. “What makes this an engineering feat is the totality of it, the accumulation of factors. The total length of miles, the total number of bridges — over 600, including six to eight long-span bridges — the total number of people who were involved (one-quarter of a million), the very short time in which they managed to accomplish it, and the extreme conditions they accomplished it under. They had very little transportation to get stuff to and from the workers, they had almost no medication, they couldn’t get food let alone materials, they had no tools to work with except for basic things like spades and hammers, and they worked in extremely difficult conditions — in the jungle with its heat and humidity. All of that makes this railway an extraordinary accomplishment.”