Milltown is marked by a spectacular 19th-century railway bridge across the river, which was part of the Harcourt Street railway line which ran from Harcourt Street to Bray. On 30 June 2004, the bridge was re-opened for the Luas light rail system which runs from St. Stephen's Green to Bride's Glen. This bridge, and sometimes the area immediately surrounding it, became known informally as the 'Nine Arches'. Milltown railway station opened on 1 May 1860 and finally closed on 31 December 1958.

The Nine Arches in Clonskeagh (Milltown) is a series of nine stone bridge arches that cross the River Dodder in Dublin, Ireland. The nine arch bridge  was built in the early 19th century by John Rennie, a Scottish civil engineer. Rennie was also responsible for the construction of the Waterloo Bridge in London and the Pont du Gard in France.

The Nine Arches were originally built to carry the Dublin to Kingstown (now Dun Laoghaire) railway line over the River Dodder. The railway line was opened in 1834, and the Nine Arches was an important part of the route. The bridge was also used by pedestrians and horse-drawn carriages.

The railway line closed in 1958, and the Nine Arches was no longer needed for their original purpose. However, the structure was saved from demolition and has since been restored. They bridge is  now a popular tourist destination and a well-known landmark in Clonskeagh.

The Nine Arches are made of limestone and are about 100 feet long. The bridge is supported by nine arches, which are spaced evenly apart. The arches are about 20 feet high and are made of a series of voussoirs. The voussoirs are wedge-shaped stones that are arranged in a semicircle to form the arch.

The Nine Arches are a beautiful example of early 19th century engineering. They are a testament to the skill and craftsmanship of John Rennie. The bridge is  also a reminder of the important role that the railway played in the development of Dublin.