Meaning of the Celtic Cross
In Irish legend, a popular tale credits Saint Patrick with the design of the Celtic cross. The tale goes that St. Patrick combined the Christian cross with the sun (or possibly the moon). This was an attempt to highlight the importance of the cross by combining it with a known Celtic symbol of life.
However, we now know that this style of Cross predates St. Patrick, and that Celtic cross designs were in existence prior to the 5th century (though perhaps not as widespread due to the fact that Irish monks had yet to raise many of the better known examples).
The massive crosses found across Ireland today were generally constructed in the name of Christianity. Other than the obvious Christian reference of the cross, various crosses contain panels with either biblical scenes, or decorative Celtic art. Traditional Irish symbols were often used for the panels, as were significant scenes from the bible, such as the crucifixion, the resurrection, Adam and Eve, and so forth.