Flying buttresses

To build tall structures, Roman architects had to build thick walls and minimize windows, leading to gloom. Key points could be buttressed with arched supports, leaving the wall thin and full of windows.
 Suger France 1137 Flying buttresses

To build tall structures, Roman architects had to build thick walls and minimize windows, leading to gloom. Key points could be buttressed with arched supports, leaving the wall thin and full of windows.