Step 1::   Builders divert the stream as much as they can with a small dam, called a coffer dam, and excavate to the bedrock so they can lay the first stones of the arch. Although irregularly shaped pieces of stone are used, with no mortar, the stones are chosen carefully so that long pieces tie together the masonry as the arch rises. In the first of these pictures, which are not the Packerville Bridge but rather an unknown bridge being built somewhere in eastern Connecticut around 1900, the right side of the arch is just beginning to form a curved shape. The timber bridge being replaced is still functional in the background.

Wetherell Collection photograph, courtesy of Quinebaug Valley Community-Technical College, People at Work Archive