Petrarch Invented the Dark Ages
A stylistic complaint about Latin prose hardened into a description of an epoch, and then of the world. It draws the map so that the lit portion falls outside the frame.
The Dark Ages were not a period. They were a branding decision, and we know who made it.
Petrarch, in the fourteenth century, looked back at the centuries between the fall of Rome and his own moment and called them dark. He meant it as a literary judgement about Latin prose style, which had declined from the Ciceronian standard he admired. It hardened into a description of an epoch, and then into a description of the world.
The trouble is what it required everyone to not look at.
Those centuries were dark only if you restricted your gaze to Western Europe. Look east in the same period, to Constantinople, Baghdad, Cairo, Córdoba, Samarkand, Timbuktu, and you are looking at some of the most luminous intellectual activity in human history.
The period Europe calls dark is the period in which the Canon of Medicine was written, algebra was constructed as a general method, the scientific method was articulated in Cairo, Ptolemy's tables were corrected against the sky, and hospitals, observatories and endowed universities were operating at a scale Europe would not match for centuries.