The earliest known cast iron dates to China in the 8th century B.C., according to research published in Advances in Archaeomaterials in May 2021. The process of casting iron involves mixing iron with carbon and other alloys, creating an iron alloy that is more brittle, but also harder.

Cast iron played a large role in Iron Age China’s agricultural development. The moldboard plow that emerged in Iron Age China around the third century B.C. used a cast-iron point to push soil away, allowing for the development of contour plowing, which reduced soil erosion.

Quenching is another process of making iron harder and more brittle that became important during the Iron Ages in Europe and Asia. Iron itself isn’t necessarily harder than bronze, but once transformed into steel, which is harder than bronze, quenching can make steel stronger.

It’s very difficult to tell when quenching began, says Erb-Satullo. He points out that The Odyssey, which the Greek poet Homer composed around the 8th or 7th century B.C., contains a reference to quenching. This comes during the scene in which Odysseus throws a sharpened and heated piece of wood into the cyclops’ eye: “as when a man who works as a blacksmith plunges a screaming great ax blade or plane into cold water, treating it for temper, since this is the way steel is made strong, even so Cyclops’ eye sizzled about the beam of the olive.”

Iron swords and daggers didn’t start with the Iron Age. King Tutankhamun was buried with an iron dagger likely made from a meteorite in the 14th century B.C., which is way before scholars would place the beginning of the Iron Age. The key innovation of Iron Age weapons was not that they used iron, but that they eventually used steel produced from new metallurgy techniques.

​​Early iron swords were not necessarily better or harder than bronze ones, but innovations like quenching helped make strong, steel swords that became more common over time. One of the most famous surviving Iron Age steel swords is the Vered Jericho, which dates to the 7th century B.C. in ancient Israel.

Even as iron and steel became more widespread, Iron Age people continued to make bronze weapons and tools, too. In addition, there were new technological developments that used older materials like gold, silver and even stone.

Gold and silver weights existed during the Bronze Age, but the first coins—i.e., imprinted metal pieces for exchange—seem to have emerged in Iron Age Anatolia, Erb-Satullo says.

The first coins appeared around 600 B.C. in Lydia, a kingdom on the Anatolia peninsula (modern-day Turkey). These coins, imprinted with images like lions, had similar weight and purity, and so may have been used as a form of currency.

The Roman Empire began to produce coins in the late 4th century B.C., starting with bronze and later shifting to silver and gold. Coins unearthed in London dating to the first century B.C., around the time the Roman Empire invaded the region, show the god Apollo on one side and a charging bull on the other.

Another Iron Age invention that doesn’t directly involve iron is the rotary quernstone. This was a new type of quern, a tool used for grinding grain by hand that has existed for thousands of years, since before 5600 B.C.

The rotary quernstone that emerged in Iron Age Britain around 400 B.C. consisted of two stones on top of each other. The top stone had a hole in it in which a person would pour grain. The user would then rotate the top stone to grind the grain between the stones, and the ground grain would spill out over the sides.

The rotary quernstone took more time to make than other querns, but ​​was able to produce grain much faster.