Carpenters would prepare and assemble the timbers of the frame in their own yard, marking the joints ready for assembly on sight. Beams, posts, joists and so on were mortised and tenoned while still on the ground.

The heavy joints were numbered with a system of Roman numerals usually made from a tool called a scribe.

The markings were slightly different from those we recognise today. In their system IV became III and IX became VIII. One theory about this method is that medieval carpenters were unable to subtract, but as timbers could be turned on-site it is more likely that they adopted their system because XI upside down becomes IX, which would not be correct.

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