Roman Arc

Roman Arcs are nice in the sence that they do not requiere clue (or concrete) to keep em together.

The top stone (also called key stone, I guess) and further weight on it keeps everything together.

To assemble the arc one needs a scafolding to lay the curved stones on before the key stone is inserted.

One problem so, is that lateral forces need to be accomodated carefully. Thats why the two collums are wedged into the base plate: to keep them from toppling over.