Complex sentence: In Gaelic Ireland, a person's wealth was reckoned by reference to the number of cattle he had, a wealthy man was reckoned to be "fear mile bo", a man of a thousand cows.
Split into simpler sentences: In Gaelic Ireland, a person's wealth was measured by the size of his cattle herd. A wealthy man was reckoned to be "fear mile bo", a man of a thousand cows.