After the civil engineer looked over the site of the proposed road and determined roughly where it should go, the "agrimensores" went to work surveying the road bed. They used two main devices, the rod and a device called a "groma", which helped them obtain right angles. The rod men put down a line of rods called the "rigor". A surveyor looked along the rods and told the "gromatici" to move them as required. Using the "gromae" they then laid out a grid on the plan of the road.