[7] Originally equipped with a central swing span, it was revised several times over the years until its superstructure was completely replaced in the late 1980s due to unacceptable vibration and the collapse of a similar bridge in Connecticut.

[8][9] In 1874 the Massachusetts Legislature authorized construction of a bridge between Boston and Cambridge,[10] and in 1882 follow-up legislation set out its location.

[12] There was still no substantive progress until 1887, when Cambridge petitioned the Legislature to compel Boston to proceed; the resulting act required each city pay half the cost, and allowed Boston to raise up to $250,000 (US$8,480,000 with inflation[13]) for this purpose, in excess of its debt limit.

The residents of the Back Bay, South End, Roxbury, and other southern sections of Boston are now connected directly, by way of West Chester park and the bridge, with Cambridge, Belmont, Arlington, and adjacent towns; and this thoroughfare in Boston, it is believed, will ultimately be the central one of the city.The bridge is named for the Reverend John Harvard, for whom Harvard University is also named, rather than for the university itself.

Much of Boston is underlain with clay, but the situation at the bridge is exacerbated by a fault which roughly follows the path of the Charles River itself.

From a depth of approximately 200 to 300 feet (60 to 90 m; 40 to 50 sm) below existing ground, is a very dense till composed of gravel and boulders with a silt-clay matrix.

[3] Originally, the bridge was built across the Charles River connecting West Chester Park, in Boston, with Front Street, in Cambridge.

[3] The original roadway contained two lanes for horse-drawn vehicles and two street car tracks, for a total width of 51.0 feet (15.5 m; 9.13 sm).

[3][28] Heavy traffic at the Mass Ave and Memorial Drive intersection on the Cambridge end of the bridge led to the construction of an underpass in 1931.

[29] An engineering study was performed by the Metropolitan District Commission (later merged into the Department of Conservation and Recreation) in 1971–1972 due to complaints by bridge users of excessive vibration.

[31] Suggestions made included strengthening the existing structure by adding either struts or plates to make the existing four beams along the length of the bridge into a stiffening truss, or to replace the superstructure with a new one, made of either steel or concrete, which would be up to current standards.

[30] The recommendation was to replace the superstructure with one weighing approximately the same in order to reuse the piers, which were in good condition.

The resulting new bridge would be of known materials and quality, such as ductile structural steel rather than brittle wrought iron, and rated at AASHO HS-20.

Repairing the existing structure would leave old wrought iron of uncertain quality and condition standing, and would not bring the design up to (then) current standards.

[36] Structural modifications included an upgrade from four longitudinal girders to six of the same shape and replacement of a stairway with a handicapped pedestrian ramp on the Boston end of the bridge.

In order to document the pre-existing structure, a Historic American Engineering Record (HAER) would be prepared.

Phase 1 would reinforce the downstream side of the bridge to allow MBTA bus traffic, and was expected to take 5 months.

[41] In the fall of 2014, the Charles River Conservancy announced that an anonymous donor would fund an upgrade of the street lights for both the roadway and both sidewalks on the bridge.

[47] "It will provide safe lighting for pedestrians and drivers, and the elements of design on the bridge will be pulled out and emphasized.

It will become a really beautiful bridge," said Renata von Tscharner, founder and president of the Charles River Conservancy.

To this date, the Harvard Bridge remains one of the most popular cycling routes in New England, with an average of over 1,000 bicyclists in each direction per day.

[50] Markers painted at 10-smoot (55.83 ft; 17.02 m) intervals give the bridge's length 364.4 smoots long, "plus one ear".

[54] During the major reconstruction in the 1980s, the new sidewalks were divided into smoot-length slabs rather than the standard six feet, and the smoot markings were painted on the new deck.

[1][22] A possible cause is that in 1958, there were ramps to Storrow Drive on both sides of the bridge, which interrupted the sidewalk earlier than it extends today.