Known by many in Spain as "O'Neill's Regiment", it was formed in 1709 from Irishmen who fled their own country in the wake of the Flight of the Earls and the penal laws and who became known as the Wild Geese - a name which has become synonymous in modern times for Irish mercenaries and soldiers throughout the world.
Swiss, Germans, Italians and Walloons were recruited but the Spanish were particularly keen to engage Irishmen because of their reputation as soldiers.
In 1806 the uniform was changed to a sky-blue coatee with yellow lining, turnbacks and trim worn with a white vest and breeches, perhaps to differentiate them from their red-coated British allies.
One facet of so many Irishmen fighting for opposing nations in Europe was that they occasionally faced each other as enemies on foreign battlefields.
The Hibernia Regiment found itself in this position at the siege of Badajoz, in 1811, when they faced the Irish Legion under the command of the French.