The spit is kept turning so that no section of the meat is exposed to the high heat for long.
The Celtic method was to spit-roast over an open fire on a hearth in the middle of the house, where a bar was set between two andirons.
Large cuts of meat, even whole animas can be cooked this way, getting thoroughly browned without being overcooked.
The Egyptians thrust a bar lengthways through a bird or a fish and a servant held this over a fire. In one tomb illustration a servant is known waving a fan over a bird, either to keep away flies or to act as a bellows.
The Greeks and Roman used spit-roasting for small game, fish, and pieces of meat, but preferred to roast their meat and fish in iron pans or clay pots, which were placed directly on the fire or on a gridiron set over glowing charcoal. It is a favorite method among the Romans, but the flare-ups when grease hit the open coals caused fire.
The Emperor Augustus created a corps of watchmen-firefighters to patrol the city watching for kitchen fires, and Roman kitchens were usually placed in separate buildings, so if a fire start, the principle structure would not burn down.
Ancient history of roasting