Historically , most arch spans had solid spandrels , meaning that the areas between arches were completely filled in -- usually with masonry -- until the advent of steel and reinforced concrete in the 19th and 20th centuries .
Historically , most arch expansions had solid spandrels , meaning that the areas between arches were completely filled in with masonry . This was true until the use of steel and reinforced concrete began in the 19th and 20th centuries .