The purpose of an Arch and a Lintel is to carry the weight of the structure above the openings such as doors, windows and passages.
For such openings, materials like wood, stone, brick, steel and concrete are used both for arches and lintels. Reinforced Cement Concrete (RCC) is preferred nowadays for its integrity and easy construction.
An arch is a mechanical alignment of wedge-shaped blocks of bricks or stones together supporting each other and successively supporting at the ends by piers or abutments.
But, arches made of RCC and steel are built as a single block without using wedge-shaped blocks.
Primarily the stability of an arch depends on the friction generated among the wedge-shaped blocks and the cohesion of mortar.