Bridging the Hudson river, to make a road over the water between New York and New Jersey, turned out to require the building a span twice as long as any other suspension bridge of its time — a marvel of  technical achievement. Little surprise, then, that it took a century from the earliest proposals until a viable design was proposed by the Swiss-born engineer Othmar Ammann. The Port Authority commissioned Ammann to build out his design, as the chief engineer for the 3,500-foot, double-decked span.

On this day, April 30, in 1931, on the 150th anniversary of George Washington’s inauguration, the GW Bridge was completed. It would open to traffic six months later.

Today, the bridge’s upper level has added two more lanes, for a total of eight. The bottom level, although planned for from the outset, opened up only several decades later, and still holds six. Together, George and its lower level six-lane addition some have dubbed “Martha” carry more than 100 million vehicles over them each year.