We planned to set up timber bridges at a constant level, at each end of all grid lines. These bridges were located using rough setting out marked with the tent pegs. Accurate setting out of the grid was marked with nails in the top of each bridge, between which we could tie string to get a constant grid line.
We decided there were some areas we could not set out the grid today, as they needed further excavation. The timber bridges would have been in the way here. (And predictably it all took longer than expected so we also ran out of time!)