- "The Lord made us all out of iron. Then he turns up the heat to forge some of us into steel."
– Marie Osmond
- "Everything has its limit – iron ore cannot be educated into gold."
– Mark Twain
After the development of bronze it was only a matter of time for mankind to realize that it needs an easy-to-find, easy-to-work-with metal on which to base its technology. Iron is the logical choice - somewhat less strong than bronze, it is nevertheless a single metal, and not an alloy, and it is found in abundance.
And so, a new generation of iron weapons rises, used by a new warrior: the Swordsman. Building upon the experience of earlier metal working, the blacksmiths are able to make these new weapons much more deadly than previous ones.
Iron Working should be a beeline target for all civilizations bent on early conquest. After their logical choice of researching Mining and Bronze Working, it takes just one more step to get a next-generation frontline warrior and start their conquest. Iron Working is furthermore required to continue to Machinery, another very important tech of the early Medieval Era.
However, if your civ isn't particularly warlike, or threatened by a powerful neighbor, you have little reason to rush Iron Working. Bronze Working already does most of the job for early military development (including revealing Iron), and Horseback Riding will give you access to just as strong a unit as the Swordsman, while also unlocking many more useful techs of the Classical Era. Leave Iron Working for later, when you'll need to research Machinery.
Forget all of this, however, and make Iron Working your number one priority if playing as the Gauls. Thanks to their love of Mines, they will likely get the Eureka for it very quickly, and what's more, their returns from it are massive! This civ couldn't care less about the Swordsman, whose niche the Gaesatae does a fine job of filling cheaply, but this technology unlocks a crucial piece of the Gallic arsenal: the Oppidum. This district allows them to defend themselves while getting a huge head start on Production, and also unlocks the Apprenticeship technology to boost their plentiful Mines, so pick it up as soon as possible.
While the use of iron has been dated back to 4000 BC, the Hittites were the first to extract the ore, smelt it and fashion weapons – thus setting off the Iron Age around 1200 BC. In Asia, iron working developed at about the same time; iron Chinese artifacts have been unearthed dating back to around 600 BC. From those two places, using iron for weapons and tools spread quickly across the globe, except in the Americas where the natives continued to hit each other with rocks.
There were two types of iron working, one producing wrought iron and the other cast iron. Wrought iron is a semi-fused alloy, tough, malleable, corrosion-resistant and able to be welded. It could be beaten into all sorts of shapes, and it was used extensively across Europe during the Middle Ages. Besides armor and weapons and tools, iron work was used to protect doors and windows with grills and bars, and even used as decoration for Canterbury Cathedral, Winchester Cathedral and Notre Dame de Paris. The French even made it into balconies and stair railings.
By contrast, cast iron is made by melting the iron ore and pouring it into molds; the Chinese were the first to use it, primarily to make beams and rods to support their elaborate pagodas and other tall buildings. Cast iron also made pretty good arrowheads and cannon shot, as the Chinese soon discovered.
In the West, cast iron working did not take hold until around the 15th Century AD, the technique apparently moving along the Silk Road from Asia to Europe. The Europeans too found cast iron perfect for making cannon barrels and cannonballs, musket barrels and musket balls. During the Industrial Revolution structural engineers found some more creative uses for cast iron, using it to construct cast-iron bridges and as framing for ever taller buildings.