"ignorant, dull," 1590s, from Boeotia, district around Thebes in ancient Greece (said to have been so called for its cattle pastures; from Greek bous "ox," from PIE root *gwou- "ox, bull, cow"), whose inhabitants were characterized as proverbially dull and countrified by their neighbors to the east, the Athenians, who thought Boeotia "a canton hopelessly behind the times, a slow canton, as the nimble Attics would say, a glorious climate for eels, but a bad air for brains" [B.L. Gildersleeve, "Pindar: The Olympian and Pythian Odes"]. The Boeotians presumably held reciprocal opinions, but their great writers, Plutarch and Pindar, though patriots, are full of praise for Athenian deeds and institutions.
Though his aim was to vindicate Boeotia, [Pindar] has probably done her a disservice, in that he has helped to immortalise the scurrilous proverb Βοιωτία ύς [Boeotian swine], which he wished to confute. ... If left to itself, the slander might have passed into oblivion long ago. [W. Rhys Roberts, "The Ancient Boeotians," 1895]