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Sixth Street
view page - Allegheny River Bridge, wooden covered, 1819-1857
view page - St. Clair Street Bridge, suspension, 1859-1892
view page - Sixth Street Bridge, through truss, 1892-1927
view page - Sixth Street Bridge, eyebar suspension, 1928-present

Seventh Street
view page - Seventh Street Bridge, eyebar suspension, 1884-1924
view page - Seventh Street Bridge, eyebar suspension, 1926-present

Ninth Street
view page - Hand Street Bridge, wooden covered, 1839-1890
view page - Ninth Street Bridge, through truss, 1890-1925
view page - Ninth Street Bridge, eyebar suspension, 1926-present

Historic American Engineering Record
"Three Sisters" Bridges
HAER No. PA-490

(Trinity of Bridges)
Pennsylvania Historic Bridges Recording Project - II
Spanning Allegheny River at Sixth, Seventh, and Ninth streets
Allegheny County

National Park Service
1849 C Street, NW
Washington, DC 20240

(Trinity of Bridges)
HAER No. PA-490

Location: Spanning Allegheny River at Sixth, Seventh, and Ninth streets,
Pittsburgh, Allegheny County, Pennsylvania.

USGS Quadrangles: Pittsburgh West, Pennsylvania (7.5-minute series, 1993), Sixth and Seventh Street bridges; Pittsburgh East, Pennsylvania (7.5-minute series, 1993), Ninth Street Bridge.

UTM Coordinates: 17/584520/4477650 (Sixth Street Bridge)
17/584700/4477750 (Seventh Street Bridge)
17/584840/4477785 (Ninth Street Bridge)

Dates of Construction: 1926-28 (Sixth Street Bridge)
1924-26 (Seventh Street Bridge)
1924-26 (Ninth Street Bridge)

Designers: Allegheny Department of Public Works: T. J. Wilkerson, consulting engineer; Vernon R. Covell, chief engineer; A. D. Nutter, design engineer; and Stanley L. Roush, architect.

Builders: American Bridge Company (Ambridge, Pennsylvania), superstructure; Foundation Company (Pittsburgh), substructure.

Present Owner: Allegheny County.

Present Use: Vehicular bridges.

Significance: These structures are the only trio of nearly identical bridges, as well as the first self-anchored suspension spans, built in the United States. They are among the only surviving examples of large eye bar chain suspension bridges in America, and furthermore unusual for having been erected using cantilever methods. The bridges' design was a creative response to the political, commercial, and aesthetic concerns of Pittsburgh in the 1920s.

Historian: Haven Hawley, August 1998.

HAER No. PA-490
(Page 2)

Project Description: The Pennsylvania Historic Bridges Recording Project II was co-sponsored during the summer of 1998 by HABS/HAER under the general direction of E. Blaine Cliver, Chief; the Pennsylvania Department of Transportation, Bureau of Environmental Quality, Wayne W. Kober, Director; and the Pennsylvania Historical and Museum Commission, Brent D. Glass, Executive Director and State Historic Preservation Officer. The fieldwork, measured drawings, historical reports and photographs were prepared under the direction of Eric DeLony, Chief of HAER.


Pittsburgh, founded in 1794 and incorporated in 1816, developed rapidly on the basis of its mineral deposits, location at the entry to the western U.S., and abundant navigable waters. Throughout the nineteenth and twentieth centuries, Pittsburgh annexed neighboring boroughs and townships, climaxing in consolidation with Allegheny City in 1907. Annexation joined the two cities' commercial interests, following paths first laid out by bridges across the Allegheny River flowing between them. [1] Chiefly through annexation, Pittsburgh's population increased from 86,000 in 1870 to 190,000 in the mid-1870s. By that decade, the Allegheny River had proved to be a major transportation route for barges filled with coal, oil, lumber, and miscellaneous river traffic. [2]

The Monongahela River had Pittsburgh's first ferry and bridge connections, but efforts to cross the Allegheny quickly followed. Prominent Allegheny City resident William Robinson, whose son was not only the first non-lndian child born in the North Side but also became the city's first mayor, owned the Allegheny-Pittsburgh ferry. His service took passengers back and forth between Franklin Road (later Federal Street) in Allegheny and St. Clair Street (later Sixth Street) in Pittsburgh. [3]

The first petitioners to build bridges across the Allegheny and Monongahela rivers received charters on 20 March 1810. After a delay in constructing the bridges, their charters lapsed. Lack of funding, related to problems chartering of banks within the state, caused the bridge companies' inaction. The legislature refused a charter application from the Bank of Pittsburgh in 1810, which had promised to fund the proposed bridge projects with $20,000.


[1] G. M. Hopkins, Atlas of the County of Allegheny, Penna., from Official Records, Private Plans and Actual Surveys (Philadelphia: G. M. Hopkins, 1876), 4; City of Pittsburgh, "Incorporation of Boroughs and Townships Now Annexed to City," 1936, in Closed Reference Map Files, State Library of Pennsylvania, Harrisburg, Pa.

[2] L. H. Everts, A History of Allegheny County, Pennsylvania (Philadelphia: J. B. Lippincott & Co., 1876), 136.

[3] Adrian J. Briggs, comp., A Chronological History of Old Allegheny City Penna. (Pittsburgh: Don Kuhl Printing Co., 1969).

HAER No. PA-490
(Page 3)

With the Bank of Pittsburgh out of the picture, the companies faced the difficult prospect of acquiring funding without the bank's assistance, delaying construction efforts until new charters could be obtained on 17 February 1816. [4]

The First Sixth Street (St. Clair) Bridge, circa 1819

The St. Clair Bridge at first endured a reputation as a second sister to the Smithfield Street Bridge over the Monongahela. The latter, an eight-span structure designed by nationally known bridge-builder Lewis Wernwag, opened in 1818 at a cost of $102,000. At a lesser price of $80,000, the St. Clair Bridge was built by a local contractor named Lothorp. [sic, Sylvanus Lothrop] It opened to traffic in late 1819, as shown by toll records for the bridge company. Although the Monongahela crossing was initially more important because of larger settlement south of the river, the St. Clair Bridge eventually became the better-known and more-used crossing as Allegheny City outgrew the South Side. [5]

Although no detailed physical descriptions or illustrations of the St. Clair Bridge remain, its design can be compared to other early Pittsburgh bridges. A nineteenth-century historian noted similarities between the later Mechanic (Sixteenth) Street Bridge and the first covered wooden structures over the Allegheny and Monongahela, suggesting that a local style or a single bridge builder -- perhaps Lothorp [sic] -- predominated in projects of the period. [6] It is known that Lothorp [sic] used an arch-reinforced wooden truss design pioneered by Theodore Burr (the Burr arch truss) on the nearby Hand (Ninth) Street Bridge. He quite possibly used this truss form on the St. Clair Bridge as well. Both bridges employed similar construction methods, incorporating iron elements into the wooden trusses, which were carried on substantial masonry abutments and piers. [7]


[4] Everts, History of Allegheny County, 135. For dates of all early charters for bridge companies in Pennsylvania, see "Bridges: List of the Bridges, Authorized by the Legislature of Pennsylvania, to be Erected by Companies, in the Order in the Several Acts of Incorporation Were Passed," in Bridge Company Accounts, 1809-1859, General Administrative and Financial Records, Record Group 2: Department of the Auditor General, Pennsylvania State Archives, Harrisburg, Pa. [hereinafter cited as Bridge Company Accounts].

[5] Frank C Harper, Pittsburgh of Today: Its Resources and People, vol. 1 (New York: The American Historical Society, Inc., 1931), 206. David Plowden, Bridges: The Spans of North America (New York: W. W. Norton & Co., 1974), 74, 239, gives 1821 as the St. Clair Bridge's opening date. In 1819, the bridge company collected just less than one-quarter of its 1820 revenues. This indicates that the bridge opened to traffic in late 1819, but does not provide a definitive completion date See "State of the Allegheny Bridge Co., from the Date of Organization, 8th July, 1816,until January 1st, 1851, Inclusive," in Bridge Company Accounts. A. Warner & Co., History of Allegheny County, Pennsylvania, vol. 1 (Chicago: A. Warner & Co., 1889), 570, notes the actual name on the charter was "A Company for Erecting a Bridge over the Allegheny River Opposite Pittsburgh in the County of Allegheny

[6] Everts, History of Allegheny County, 135.

[7] Harper, Pittsburgh of Today, 206.

HAER No. PA-490
(Page 4)

In the St. Clair Bridge, Lothorp [sic] used wooden truss spans of varying lengths to achieve a total length of 1037'-0". The wooden superstructure included four spans each 185'-0" long, one 170'-0" long, and one 137'-0" long. Iron bars 1" in diameter provided vertical ties between the floor system and the arches above. Stone piers supported the spans, which were joined to each other by removable iron bolts in case a particular span needed repairs [8]. (Some of the masonry, in fact, remained in use through the third bridge on the Sixth Street site.)

The St. Clair Bridge's opening was celebrated with a banquet eaten across virtually the entire length of the structure [9]. The bridge was known as a promenade for young people, a social event that enhanced its popularity during daylight hours. Lit by oil lights extinguished at midnight, it was considered a safe passage by day but not hospitable for night-time crossings. The bridge company charged two cents for pedestrians. As its backers had hoped, trans-Allegheny traffic soon preferred the St. Clair Bridge over the ferry, forcing the latter into obsolescence. [10]

Despite the success of land transportation crossing area rivers, alternative methods continued to find use in the mid-nineteenth century. The state-constructed Pennsylvania Canal spanned the Allegheny on a wooden aqueduct at Eleventh Street built in 1829, but in 1843 weakness in a fire-damaged pier forced its closing. The city of Pittsburgh could not persuade the state to repair the structure, but instead received authorization to charge tolls to finance the work locally. John A. Roebling designed a cost-effective reconstruction using wire cables to carry the roadway, finishing the work in 1845. Roebling's reputation for suspension bridge design and his ability to finish a bridge within its original budget of $62,000 impressed local observers. [11]

The suspension aqueduct charted a potentially lucrative innovation for the region. It was the first such structure in the country, carrying a wooden flume over seven spans of 162'-0" each. Accounts vary, but the aqueduct seems to have continued in service until at least the mid-1850s, and perhaps as late as 1860. One local historian recorded that the city lost money despite the tolls, helping to precipitate the canal's demise. A bridge enthusiast commented on the structure's success, however, and noted its use until 1860. [12] Regardless of the precise date of abandonment and degree of success, the aqueduct began to deteriorate soon thereafter.


[8] W, G. Wilkins, "The Reconstruction of the Sixth Street Bridge at Pittsburg, Pa.," Proceedings of the Engineers' Society of Western Pennsylvania 9 (1895): 144; Warner, History of Allegheny County, 206.

[9] Leland D. Baldwin, Pittsburgh: The Story of a City (Pittsburgh: Univ. of Pittsburgh Press, 1937), 205.

[10] Everts, History of Allegheny County, 135; Wilkins, "Reconstruction of the Sixth Street Bridge," 143-44; and Warner, History of Allegheny County, 570.

[11] Plowden, Bridges, 74.

[12] Warner, History of Allegheny County, 571, claimed that financial hardship caused the canal's closure while Plowden, Bridges, 74, called it a great success.

HAER No. PA-490
(Page 5)

The First Ninth (Hand) Street Bridge, 1840

In 1835, the St. Clair Bridge and the aqueduct provided the only Allegheny River crossings. As the cities of Allegheny and Pittsburgh continued to grow, leading citizens obtained a charter for constructing a third structure. The 1836 charter permitted the Pittsburg & Allegheny Bridge Company to build a bridge joining Hand Street (later Ninth Street) in Pittsburgh with Chestnut Street (also known as Greyasoto Lane; later Anderson Street) in Allegheny. The company chose Pagan, Alston & Company to construct stone work for $37,000, paid an unknown contractor $10,000 to construct approaches, and hired Le Baron & Lothorp [sic, William Le Barron & Sylvanus Lothrop] for the superstructure, paying $33,000. It appears that Lothorp [sic] was the same contractor who constructed the St. Clair Bridge. [13]

The Allegheny's fast-moving current presented a difficult problem for bridge builders. Although the original drawings had been lost when the bridge was reconstructed in 1890, Gustave Kaufman, an engineer involved in replacing the structure, found exceptionally good alignments and elevations but poor masonry work. The four piers measured 9'-0" by 35'-0", with sides battered 1:12, semi-circular nosings on their upstream and downstream faces, and arch skewbacks 4'-0" longer than the pier tops. The masonry price of $7 per cubic yard might be considered fairly expensive given the poor workmanship. The lime mortar deteriorated rapidly, and the Freeport sandstone suffered from exposure to the river's current. Areas of masonry not exposed to water and ice remained in better condition than the piers. [14]

The Panic of 1837 slowed construction, but the company continued foundation work and waited for an economic recovery. Local opposition, perhaps because residents feared that another cross-river construction would initiate a repeat of the powerful flood of 1832, delayed work. The 1832 flood was thought to have been intensified by obstructions put in place to protect structures erected by bridge interests. The Pittsburg & Allegheny Bridge Company temporarily lost permission to build a Hand Street abutment until the company guaranteed in 1838 that its structures would not impede river flows. [15]

The company abandoned its plan to sell stock in the venture and borrowed money to complete the bridge. In 1840, the firm began recording toll collections for passage. To gain authorization for the Hand Street project, the bridge company paid half of the cost for a bridge that carried the West Pennsylvania Railroad over a canal on the Allegheny side, near what became Canal Street. The company also paved a road from the canal to the bridge. A tunnel through the Allegheny approach had to be bored to make way for the Pittsburg & Western Railway's tracks. The railroad gained a 12'-0" by 16'-0" opening about 20'-0" from the northern


[13] Gustave Kaufman, "The Reconstruction of Ninth Street Bridge, Pittsburg, Pa.," Proceedings of the Engineers' Society of Western Pennsylvania 8 (1892): 189, 192.

[14] Kaufman, "Reconstruction of Ninth Street Bridge," 190-92.

[15] Kaufman, "Reconstruction of Ninth Street Bridge," 191.

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Last modified: 05-May-2003

HAER Text: Haven Hawley, August 1998; Pennsylvania Historic Bridges Recording Project - II
visit site - "American Memory" at Library of Congress
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