In old and medieval Dublin Kilmahonock’s ford crossed the Liffey nearby Island Bridge and west of the walled city with its watchful sentries. A sylvan location, with meadows and woodland gently sloping to the meandering river, it became, with the tightening English grip, a strategic point for controlling entry to the city and in the middle of the fifteenth century Kilmainham Bridge was built, reportedly a stone structure. The bridge was swept away by floods in 1545.
Sir Henry Sidney, Lord Deputy of Ireland and ruthless suppressor of rebels, rebuilt the bridge in 1577, embellishing the stone structure on the western side with the armorial bearings of the reigning Queen Elizabeth l. Sidney or Island Bridge spanned the river in eight stone arches with a narrow deck. That bridge stood for more than two hundred years and a weir nearby allowed for the establishment of flour mills, breweries, fisheries and bleachers - two flour mills are recorded in the 1500s.
Island Bridge water had a reputation for keeping well on long journeys and from the 1730s was piped across the bridge to the northside of Dublin by means of a ‘forcing engine’. In time the infamous Liffey floods took their toll on the bridge and despite repairs a replacement was deemed necessary. On April 14, 1780 Parliament granted 4,000 guineas for the completion of the circular road and the rebuilding of the Island Bridge. The Commissioners of the Circular Road decided upon a structure of three arches but having expended considerable time, all of the money and incurring debts the project was abandoned with two piers built to the height of low water mark and the abutments half finished.
When in 1785 the decision was made to use the turnpike tax to repay the debts and once more embark on the rebuilding of the Island Bridge, citizens begrudged this use of their money. Around 1787, three of the arches of Sidney’s Bridge were carried away by floods and the bridge was left in a ruinous state. One dark November night, a boy driving a carriage home, turned onto the bridge only to fall to his death in the river. The urgency of repairing the fractured water supply caused a repair of the bridge using timber trusses and laying a deck across the remaining stone piers and the water pipes laid upon these.
In 1790 Parliament once more granted money for the completion of the bridge and John Blaquiere, soldier, politician and amateur engineer undertook its management. Blaquiere worked to the design of Scotsman Alexander Stevens. The foundation stone was laid in July 1791 and in February 1792 the public was informed of their last opportunity to attend between 7 and 11 a.m. to buy fresh salmon - it was necessary to close some of the Island Bridge fisheries. The bridge opened around October 1792, connecting suburban Island Bridge and the Phoenix Park to the north western road. Sarah Bridge was acclaimed for its elegance of design and standard of workmanship, complementing perfectly the vista of the parkland, river and the fine, blue tiled houses of its surrounds.