the romans employ glass windows (around 50 A.D.)
The Romans discovered how to produce rolled plate glass. Glass mass was poured onto a flat stone table and subsequently polished. The dimensions were fairly small, and the glass not quite transparent.
Of course, it was a luxury product, mainly used in opulent villas and large bathing complexes. In the hot rooms of the baths, obviously it was desirable to let light in without allowing the heat to slip out. In the baths of Pompeii, windows have been found still in their original positions.