While St. Patrick brought Christianity in to the Irish, the pagan and Celtic traditions that founded Ireland have always been strong. One of the key ideas involved handfasting.
Handfasting was sort of a 'trial marriage' for a year. If at the end of the year either partner decided it wasn't quite right, they left with no committment. Nowadays, the handfasting is included in some ceremonies with the ribbons binding the hand of the bride and groom together.
Irish Wedding Traditions