The Pennsylvania Avenue Bridge (Source: Library of Congress).

Mathew Brady photograph of Montgomery Meigs in 1864 (Source: Library of Congress).

The bridge during the Civil War (Source: Library of Congress).

The bridge in the 1860s (Author's collection).

The bridge in the late 1890s (Source: Library of Congress).

The rebuilt bridge, photographed in 1993 (Source: Library of Congress).

The original arched water mains were still visible underneath the bridge in this photograph from 1993 (Source: Library of Congress).

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Many people know about the old Aqueduct Bridge that preceded the Key Bridge over the Potomac and that we profiled previously . But there's another Georgetown bridge that still carries both water and traffic safely across a separate body of water, thus serving as a functioning aqueduct. The bridge in question is the one carrying Pennsylvania Avenue over Rock Creek and the Rock Creek & Potomac Parkway at the eastern edge of Georgetown.For the first half of the 19th century, Pennsylvania Avenue's western terminus was at Rock Creek. If you wanted to continue over the creek to Georgetown you had to go north and take the rickety wooden M Street bridge, the historic crossing that had given the eastern stretch of M Street in Georgetown the name "Bridge Street." The additional Pennsylvania Avenue crossing was proposed as early as 1836 but it didn't come about until 22 years later and not primarily to facilitate travel along the Avenue. Instead it was the result of a fire.On the morning of Christmas Eve in 1851 a watchman on the U.S. Capitol grounds noticed smoke coming out of a window. It was the room occupied by the Library of Congress. The watchman summoned help, and eventually seven fire engines arrived from all parts of the city, but they were stymied by the cold and the lack of running water. Though the fire was put out by mid morning, some 35,000 books were destroyed. Thecommented, "We must say that we consider the system adopted by the Government for the protection of the public buildings and property as essentially defective, as the various conflagrations which have taken place...must prove."Until then Washington's water had come from local springs and wells, and the city desperately needed a more reliable system. After the Christmas Eve fire Congress finally appropriated funds to build a new system for delivering "an unfailing and abundant supply of good and wholesome water" to Georgetown and Washington City.The job of constructing that system fell to Captain Montgomery C. Meigs , a man of exceptional drive, intellect, irascibility, and arrogance, who had been fascinated by engineering from an early age. When he was six years old, his mother described him as "high-tempered, unyielding, tyrannical toward his brothers, and very persevering in pursuit of anything he wishes." He graduated fifth in his class of 49 at West Point (the best engineering school at the time) and assisted Lt. Robert E. Lee , whom he greatly admired, in surveying the Mississippi River before he was called to Washington in 1852. A little luck and a few well-placed connections landed Meigs the job of planning the city's new water system and supervising its construction.Meigs devised an elaborate system whereby water would be diverted from the Potomac River at Great Falls and channeled into reservoirs to be filtered and piped down to Georgetown and Washington. The entire system, from Great Falls to the Navy Yard, was 18.6 miles long. Most of it was in an open conduit, but 11 tunnels and six bridges were also required. Of the six bridges, the largest was the Cabin John Bridge, the longest single-span masonry arch in the world at the time, which we previously profiled . Next to the Cabin John Bridge, the most magnificent structure along the aqueduct route was the Pennsylvania Avenue bridge.Meigs chose a daring and elegant design for the in-town bridge. He would use the very pipes that carried water into the city as support for the bridge itself. Two dramatic arches made of 48-inch-wide cast-iron pipes were flung 200 feet across the Rock Creek valley and shored up by massive stone piers on either end. Each arch was made up of 17 twelve-foot-long pipes carefully milled and fitted together with watertight precision, each joint held together with a ring of forty bolts. The pipes were lined with wooden staves to keep them from freezing in winter, and an iron truss was built on top of the arches to support the wooden deck of the bridge. Heavy traffic on the bridge meant that the wooden deck would wear out and have to be replaced every three years.Construction of the bridge began in 1858 and finished up in 1860. It was quickly recognized as an engineering marvel. "Among the public works now in course of completion at Washington one of the most remarkable, though least known, is the Washington Aqueduct Bridge over Rock Creek, at the western end of Pennsylvania avenue, now nearly completed from the designs and under the direction of Capt. Meigs," thereported in 1860. The bridge was as beautiful as it was astonishingly practical.The bridge also served as a key source of much of Georgetown's water. Parts of Georgetown were too high to be fed water from the main aqueduct solely by gravity, so Meigs built a special high reservoir at Wisconsin and R Streets , where the Georgetown branch of the DC Public Library and its renowned Peabody Room are now located. A great pumping engine installed in the western pier of the Pennsylvania Avenue bridge diverted water from the main aqueduct and pumped it up to the reservoir.But what was to be the name of this great and important bridge? As early as 1861, it was being called the Meigs Bridge, but ironically that name never really caught on—ironically in that Meigs had been as vain as he was brilliant. He had his name engraved on the side of Cabin John Bridge and stamped into numerous metal fittings throughout the aqueduct system, yet few people called his bridge the Meigs Bridge. Also known as Bridge No. 6, the span was sometimes called the Tubular bridge or the Aqueduct bridge, but usually it was just the Pennsylvania Avenue bridge over Rock Creek.Inevitably, people would come to question whether those giant water pipes could really carry the load of the bridge safely. In 1876 the army engineer in charge of the aqueduct proposed replacing the bridge because he thought it would collapse and cut off the city's water supply. Needless to say, Meigs was livid. He fired off letters to the Senate District of Columbia committee and the chief of engineers arguing that "a train of heavy locomotives could run daily and hourly over the bridge, so far as the safety of the aqueduct mains are concerned." A study was commissioned that agreed with Meigs that the pipes were sound and strong. The bridge would remain unaltered for another 40 years.Strong as it was, the span was very narrow, and it was only a matter of time before it needed to be widened and strengthened. An 1898 study on widening the bridge marveled at its gracefulness and suggested the best way to augment it would be the construct two more iron arches just like the existing water mains to make it wider. That proposal was never adopted, but finally after funds for a new bridge were authorized in 1913, a new steel girder bridge was proposed as a replacement. The U.S. Commission of Fine Arts objected to the thought of eradicating the graceful arch and insisted that the new bridge also be arched. In the end, the superstructure of the old bridge was removed and a new wider bridge built over the original water mains, which remained in place but no longer bore the weight of the bridge. The new structure, which still stands, was completed in 1916.In July 1916 the District's commissioners formally named the newly rebuilt bridge in honor of Meigs, but once again, the official name didn't take. News articles in the 1920s occasionally refer to the Meigs Bridge, but then the name seems to have been forgotten. To this day, few people crossing the bridge realize who Gen. Montgomery C. Meigs was or that, due in no small part to his engineering skill, part of the city's water supply still travels under their feet through gracefully arching cast-iron pipes laid in place over 150 years ago.Sources for this article included D.C. Department of Highways,(1956); William C. Dickinson et al., eds.,(2001); Donald Beekman Myer,(1974); Pamela Scott,(2005); and numerous newspaper articles. click on this link and choose "Get Streets of Washington delivered by email" from the Subscribe Now! box on the upper right hand side of the page.