We can assume that the first real forge of ancient times was a hole in the ground with a way to draft the fire from below.
Of course, the first metalsmiths probably didnt work in iron (black-metal) but rather copper and its alloy,
bronze - and
so there developed the bronze age. Later came the iron age - and the blacksmith.
In order to accomplish their work, the smiths need the metal very hot. Hot metal is much more
malleable. Coal and charcoal were the fuels of choice (depending on availability). In order to make the fires hot
enough, smiths found that drafting the fire with air (oxygen) from below, the heat could be intensified.
During the fourth century AD, a single chamber bellows along with the air valve was developed.
During the seventeen century, a second chamber was added to the bellows, creating the Great Bellows.
The bellows was used throughout Americas colonial period and beyond.
The industrial revolution brought about the blower, an encased fan, which would direct
air to the fire in an efficient manner. These blowers were hand cranked but for the larger industrial shops they could be
adapted to a plenum (air chamber) and the output controlled by a valve. The drive for these adapted blowers were leather
belts, driven by steam engines. In later times, the steam driven belts were replaced by electric motors.
Today, there are the very portable propane forges
which require no blowers and are used in small
shops and by farriers.
Some come with ports at each end so long bar stock may be inserted into the forge. A more effective way to setup the
propane forge is
with two propane tanks.
Oxyacetylene and oxygen-propane torches are also used by modern blacksmiths to heat only a very small
areas of metal (like bar stock). Then, with twists and reverse twists, effects like the bar just below can be achieved.