its called a flying buttress

To build a flying buttress, brick, wood, stone, and limestone is needed.

A flying buttress is not a feature of Romanesque architecture.

A flying buttress is a form of buttressing most strongly associated with Gothic church architecture. Flying buttress systems compose of two parts including a massive vertical masonry block on the outside of a building and a segmental or quadrant arch bridging the gap between the buttress and the wall.

to support walls.