You have to support the structure (the actual arch) using a wooden form up to the point where you insert the keystone, after which the arch will be self supporting.
Hankins Stone Arch Bridge was created in 1905.
Lalino Stone Arch Bridge was created in 1870.
Tusten Stone Arch Bridge was created in 1896.
Pithole Stone Arch Bridge was created in 1899.
Stone Arch Bridge - Minneapolis - was created in 1883.
Newport Stone Arch Bridge was created in 1853.
Woodward Road Stone Arch Bridge was created in 1887.
Elm Grove Stone Arch Bridge was created in 1817.
Moore Road Stone Arch Bridge was created in 1887.
Elm Street Stone Arch Bridge was created in 1900.
Ruhle Road Stone Arch Bridge was created in 1873.
Mill Street Stone Arch Bridge was created in 1900.