There have been four bridges across the Molonglo River at Commonwealth Avenue. The first three were constructed before Lake Burley Griffin was created. In order to create Lake Burley Griffin, the Molonglo River was dammed and Scrivener Dam constructed. Prime Minister Sir Robert Menzies officially inaugurated the lake on 17 October 1964.

The first was a low level wooden trestle, completed in 1916. This was destroyed in the floods of 1922, which also breached the southern embankment and created a billabong. The second bridge was built over the billabong, using materials that had been intended for a bridge near Kings Avenue but not on the Avenue alignment. It was built using three NSW 'Leychester' type trusses.
The third bridge was a modification of this, by raising the bridge by a metre and adding a fourth truss. Finished in 1924, this bridge was seriously damaged in the 1925 floods, and was repaired and lengthened by a fourth truss in time for the opening of Parliament in May 1927. The fourth bridge was constructed 1961-1963 and opened for traffic in November 1963.

Commonwealth Avenue ... named for a reason

Commonwealth Avenue and the bridge it passes over were not designed or named as they are by accident. The design and naming of the major features of Canberra's inner city triangle as well as the suburbs and main roads radiating from it were a vital part of designer Walter Burley Griffin's plan in which both the layout and the names of the suburbs and the roads that connected them were all deeply symbolic.
The three points of Griffin's triangle were the City Centre, Capital Hill and what is now the roundabout at Russell. The City Centre, now more commonly known as City, was intended to be and still is the business hub of the Canberra. Capital Hill was to be the seat of National Government - Parliament House was built there in the 1980s - and Russell was to be the shopping area. Of the three axis points, the latter is the only one to not have been developed in accordance with the Griffin master plan.
The three axis points were symbolic of the British Government (City Centre), the Commonwealth of Australia (Capital Hill) and the people of Australia (Russell). The circuit at the axis of the City Centre was named London Circuit, after the seat of British Government, which the City Centre symbolised. Capital Hill and Capital Circuit at the locality were thus named as they signified the purpose behind the creation of Canberra - to be Australia's new capital city with the Governmental function centralised there. The third axis point, at the intersection of Kings Avenue and Constitution Avenue, was to have a produce market at the centre of its circuit. That is the one key aspect of Griffin's symbolic design for Canberra that inexplicably and unforgivably never eventuated.
The three axis points were joined by three grand avenues - Constitution Avenue, which symbolised the link between the Australian people and the British Crown via the Australian Constitution; Commonwealth Avenue, which symbolised the Legal and Political connection between Gt Britain and Australia as the mother country and a member of its commonwealth; Federal Avenue (later changed to King Avenue), which symbolised the Federation of Australia that unified the people of the various states of Australia as a single nation via the Federal Government.
The major Government buildings were placed - and remain today - within the boundaries of those three axies in what became the suburb of Parkes, which was appropriately named after Sir Henry Parkes, a man whose vision of a unified federation of states coming under a single national Government was the catalyst behind the creation of the city of Canberra.

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