Irish flag of early 1700s

Use of the harp as an Irish heraldic device can be traced to the 16th century. A gold harp on a green flag was used by Eoghan Rua Ó Néill (Owen Roe O'Neill) in 1642, when he commanded Irish Confederate soldiers during the so-called "Irish Confederate Wars", but was recognized as the colour of Ireland only with the Rebellion in 1798. The harp pillar by the 17th century was shaped into a grotesque head of a mythological beast. During the 2nd half of the 17th century, it was further transformed into a female head and torso. In the 18th and 19th centuries, the figure acquired a pair of wings, one of which formed the neck of the harp. The figure became known as the "Maid of Erin", and became incorporated into the British arms representing Ireland. - Wikipedia