A New Year's Eve reveller is fighting for his life after being attacked by up to six people.
The 20-year-old is in Beaumont Hospital, where his condition is described as critical.
A man and a woman are being questioned by detectives over the apparently random attack, which happened on a pedestrian bridge at Priorsgate, Saint Dominic's Road/N81 in Tallaght, at approximately 4am.
"He was taken from the scene to the Adelaide & Meath Hospital, Tallaght, and later transferred to Beaumount Hospital where he remains in a critical condition," said a Garda spokesman.
"A male, 23 years, and a female, 20 years, were arrested, in connection with this investigation and are currently detained at Tallaght Garda Station under the provisions of Section 4 of the Criminal Justice Act 1984."
Gardai have appealed for any witnesses to come forward.