In this photo, you can see a double wythe brick wall cut right down the middle.
Middle English from Old English withthe(“withe”)
A wythe of brick is a single vertical assembly of units. In this case, and typical with above grade exterior or even interior demising walls in Capitol Hill the wall is a double wythe.
You can see a perfect crosection of the bedding mortar and stretcher mortar between bricks. The vertical joint between wythe is the collar joint.
In this picture you can see where a wall was dismantled and you can see a typical functional assembly of common brick. Here is well you can see this is a double wythe brick wall. We’re in the picture above you can see
the bedding mortar between the Shiner faces of the brick, in this picture you can see the prepend mortar, in section exposed, between the rowlock faces of the brick.
You can also see the otherwise, normally completely hidden collar joint between the two wythes.