Final answer:
Flying buttresses in the Middle Ages served the purpose of supporting the weight of the walls and roof of a building. They also allowed for the inclusion of larger windows and more natural light, resulting in increased interior illumination.
Step-by-step explanation:
The purpose of a flying buttress in the Middle Ages was to support the weight of the walls and roof of a building. They were architectural elements designed to redirect the forces from the pointed arches to the ground, thus stabilizing the walls and carrying the pressure of the lateral thrust. Flying buttresses were essential in allowing for larger windows and more natural light in a building, as they allowed for thinner walls in the Gothic style, which in turn facilitated the inclusion of more stained glass windows and increased interior illumination.