Line and Interior Design,
Lines in interior design are a good way to create perspective of space helping it look longer (vertical) and/or wider (horizontal) with the use of different types of lines- this creating a sense of direction.
The Gothic era is best known for their high arches emphasizing in the center of the ceiling. They used grandiose vertical columns from floor to ceiling, diagonal lines for the ceilings, as well curved lines used in windows and flooring.
This architecture (see in pic above) first flourished in Europe specifically in 12th mid-century France build by a new dynasty of Kings, who also allied with their bishops to create a new architecture that promoted their wealth, power and religious faith.
It's easy to incorporate the line element in interior design in different forms such as including the architecture, wall paper, flooring, furniture helping you enhance any size of space.