The Middle Ages (especially the early middle ages) are often pejoratively referred to as the "dark ages" because of the relative paucity of historical records, but what about technology? What notable technological advancements occurred during this period?
First, it should be stated that the exact timeframe of "The Middle Ages" is not clear cut. That being said and taking the Roman Empire as the base line, here we go.
These are technologies or methods that Romans did not know and that Europeans adopted during "the Dark Ages" (what a misnomer).
And before anyone starts: "Wait, that tech was developed by someone who was not European." That does not matter. Do you think the Romans developed everything themselves? No. Technological advancement is technological advancement.
Source: Mostly James Hannam's "God's Philosophers: How the Medieval World Laid the Foundations of Modern Science".