The Middle Ages were a thousand-year dark age of ignorance and stagnation

This one is a church-history claim rather than a Bible-verse claim, so it doesn't anchor to a single reference the way most entries do, but it earns its place because it teaches something every other entry depends on: that church history is knowable and worth checking rather than a thousand-year blank to wave off. The "dark" label has a strange origin that undercuts the popular version on its own. The 14th-century poet Petrarch coined the framing not to describe technology or theology at all, but to complain about the quality of Latin literature in his own lifetime, comparing it unfavorably to classical Rome. Centuries later, largely through 17th-century English polemic against the medieval Catholic church and then Enlightenment writers flattering their own age by contrast, that narrow literary complaint got stretched into "nothing of value happened for a thousand years."

What actually happened in that period cuts hard against the stretched version. Monasteries such as Cassiodorus's Vivarium ran scriptoria that copied and preserved classical Greek and Roman texts that would otherwise have been lost outright. Out of monastic and cathedral schools grew the first universities: Bologna around 1088, Oxford by the 1090s, Paris by roughly 1150 or 1200, training theologians, lawyers, and physicians centuries before the Reformation existed. The period also produced sustained, serious theological and philosophical work (Anselm, Aquinas, the Oxford Calculators) and reform movements from inside the church, Cluny, the friars, Wycliffe, Hus, the Devotio Moderna, that were already pushing back on corruption long before 1517.

None of that means the period was some hidden golden age. Real corruption in the medieval church existed, and the Reformation had real grievances to answer, so the correction isn't "actually it was wonderful." It's that "a thousand years of nothing" is itself a constructed narrative, first aimed at literary style, later repurposed as anti-Catholic and Enlightenment shorthand, and it collapses on contact with what monasteries, universities, and medieval scholars were actually doing during those centuries.