My apologies to this forum if my comments have engendered any controversy, that was certainly not my intention.
To address the orignal poster's question, it should be pointed out that the vast majority of garden and entranceway gates, whether custom or mass produced, are fabricated from hollow goods, primarily due to weight considerations. For this reason, tubing and pipe - hollow goods - are the most common starting materials, at least for the framework.
Although weight mandates the use of hollow goods in most gates, most bends are done in stock that has relatively thick walls because thin walls tend to kink, or flatten excessively, along the inner radius. Furthermore, due to the difficulty intrinsic to heating and handling longer workpieces, most bends in hollow goods are done cold, a fact that blurs any distinction between forging and fabricating.
The most simple method of forming a radius in tubing or pipe is to anchor one end, then force the other around a mandrel. A mandrel can be anything with the desired radius capable of withstanding the pressure of having the workpiece bent around it. The various mechanical and hydraulic benders found in most shops fall into this category, but most cannot form longer radiuses with a single bend and must be used incrementally to form a radius in longer stock. For this reason, most benders are relaively inefficient in terms of both accuracy and time management.
For longer bends in hollow stock, I use a compass to soapstone the desired radius atop a steel layout table, forge a mandrel from 1/2" x 1 1/2" to match the radius, weld it securely to the layout table, weld an anchor on one end of the mandrel to hold it in place, place one end of the workpiece between the anchor and the mandrel, then use a cheater pipe and smooth, even, people-power pressure on the free end of the workpiece in order to force it around the radius formed by the mandrel. This method is labor intensive and time consuming to set up, but it is satisfactory for turning out multiples of a single radius in hollow goods. Many of the radiuses in my screens are formed in this manner.
As an aside, it is sometimes necessary to form an edgewise radius in flat bar stock to match the radius one has formed in hollow stock. (e.g., when fabricating a secondary frame) Should this become necessary, it is easiest done hot and around the same mandrel one uses to form the radius in the hollow stock because it is maddening and extremely time consuming to exactly match a long radius in light bar stock using only a forge, hammer and anvil. :D