Medievals knew the Quran arrived piecemeal via Gabriel during Ramadan.

Evidence

In a sound statement by Peter the Venerable, the Qur’an was described (to Muslim readers) as supposed by them to be ‘what was sent down from Heaven by God and delivered by Gabriel to your Prophet, not all at once, but bit by bit, through the parts of the month that among you is called Ramadan’. — Norman Daniel, Islam and the West, 198