You need to read the given passage and construct a question about the information present in the passage. The question should be answerable from the passage. Most importantly, only those questions are allowed whose answers cannot be determined from a single sentence. Do not generate questions that require only a single sentence to answer. Instead, try to combine two sentences and create a question from that combination. Do not create open-ended questions, i.e., the answers to them cannot be found precisely from the information provided in the passage.

Paragraph- Sent 1: Ireland has been inhabited since very ancient times, but Irish history really begins with the arrival of the Celts around the 6th century b.c.
Sent 2: , Ireland's first documented invasion.
Sent 3: They brought with them iron weapons and chariots and codes of custom and conduct that quickly became dominant in the country.
Sent 4: This is the period of myths and legends, later romanticized by Irish writers, that still exercise their power today.
Sent 5: The Celts were organized along a family- and clan-based system, and Celtic Ireland became a series of independent kingdoms.
Sent 6: Nominally these kingdoms acknowledged an elected High King, with his seat at fabled Tara, as overlord.
Sent 7: There were no towns, and the cow was the medium of exchange.
Sent 8: Learning was revered, games were played, and the poet was held in awe.
Sent 9: Law and religion were important in Celtic culture.
Sent 10: The religion was druidic, and the law was an elaborate written code, interpreted by a class of professional lawyers known as brehons.
Sent 11: The brehon laws gave women a high status — they could own property, divorce, and even enter the professions.
Sent 12: Christianity and a Mission to Europe St. Patrick first came to Ireland as a prisoner, captured in an Irish raid on a Roman settlement in Britain.
Sent 13: He eventually escaped and returned to Ireland as a missionary in a.d.
Sent 14: By the time of Patrick's death in a.d.
Sent 15: 465, the whole country was effectively Christianized — a peaceful process, without a single martyr, which speaks for Patrick's natural diplomacy as well as his powers of persuasion.
Sent 16: Many legends surround his mission.
Sent 17: It was St. Patrick who used the example of the shamrock to explain the Christian Trinity to King Laoghaire and an assembled crowd at Tara.
What was Ireland's first documented invasion?