The methods of procuring sap and making syrup used by the Native Americans and early settlers relied completely on natural conditions. Reed, bark, or wood spouts were used to draw off the sap into clay or bark vessels. The sap was boiled into syrup in large kettles, usually suspended by a metal rope hanging from a pole, over a constantly stoked wood fire. The pole was held up by two forked stakes. By the mid-1800s much of the process was brought indoors, initially in an open shed where the kettles were placed underneath the roof but still hung over an open fire. Later, enclosed structures and more efficient means of moving the sap from the trees to a holding tank and then to an evaporator were developed. By the late nineteenth century metal evaporators had been introduced. They were invented by David Ingalls in Dunham, Quebec, and soon updated and adopted by New England sugar makers. This technological innovation, along with others, allowed for the development of commercial maple syrup production. By the twentieth century the making of maple syrup had moved beyond the backyard woodlot.