People tend to understand the world through the development of narratives – we tell stories about the past, the present, ourselves, others, and the world. That is how we make sense of things. I always find it interesting, the many and often subtle ways in which our narratives distort reality. One common narrative is that the past was simpler and more primitive than it actually was, and that progress is linear, objective, and inevitable. I remember watching The Day the Universe Changed with James Burke when in one episode he declared that the Dark Ages were a time of great technological advancement. This seemed at odds with what I had been told, but I later confirmed this view that the so-called “Dark Ages” were maligned by later Renaissance writers congratulating their own progress.

The same is true of our image of technological advancement, that it’s objective and inevitable. This became more clear to me when researching my latest book, The Skeptics’ Guide to the Future. One story in particular is the sequence of the material ages – the stone age giving way to the copper age, then bronze age, and finally iron age. Metallurgy was clearly a huge technological advance, and did progress significantly over time. But this sequence was not strictly linear, older technologies persisted alongside newer technologies for different applications, and sometimes technological shifts are more of a lateral move than a clear advance.

The biggest example from the sequence above is the transition from relying mainly on bronze for tools and weapons to iron. Iron, it turns out, is not objectively better than bronze for many applications. Bronze is actually a very useful metal – it can be cast, it is easy to work with, it is strong, and it doesn’t rust. That last feature, not rusting, makes it superior to iron for many applications, even into the Renaissance (until the development of stainless steel). Bronze is actually stronger than iron and can be worked more easily, at a lower temperature. Until the development of carbon steel, there was no reason to favor iron over bronze. Why, then, did the change happen?

A recent archaeological discover reflects the true reason that the bronze economy collapsed. Iron does have one big advantage over bronze – it is one element. Bronze is an alloy of copper and tin. That may not seem like a big deal, but when you are trying to run a civilization with bronze that means you need to maintain distant trade routes for both metals, and bring them together to make bronze. The find is a 2,000 year old shipwreck off the coast of Uluburun in modern-day Turkey. The ship was full of tin ore, tons of it. Scientists have been able to trace a third of the tin to a pastoral community in Uzbekistan in Central Asia.

The ship, in fact, is a snapshot of a complex trade route, that sourced tin from multiple distant locations, and then delivered it to multiple destinations throughout the Mediterranean. This was a long distance complex trade route over land (2,000 miles over land) and sea. But such a route was worth the trouble, because tin was necessary for making bronze, which was incredibly valuable. Study author Frachetti said:

“It appears these local miners had access to vast international networks and — through overland trade and other forms of connectivity — were able to pass this all-important commodity all the way to the Mediterranean.  It’s quite amazing to learn that a culturally diverse, multiregional and multivector system of trade underpinned Eurasian tin exchange during the Late Bronze Age.”

Copper was more common than tin, but still had to be sources from various and often distant mines, often located far from the sources of tin. Also keep in mind what Frachetti is saying – the tin was not put on a transport and sent 2,000 miles away. Rather, it worked its way through a complex network of international traders.

The Uluburun wreck also provides a clue, or at least an example, of why the bronze age collapsed. It was not because iron was superior – it was for the same reason we are experiencing inflation today, supply chain issues. That vast Eurasian trading network was impressive, but also fragile. A lot could go wrong along that distant supply chain. War could break out, disrupting a critical link in the chain for years. In short, as civilization and the demand for bronze grew, it became too difficult to maintain a reliable supply chain of raw materials. People started relying on iron not because they wanted to, but because they had to. It was an inferior metal, but at least the supply chain was vastly simpler.

The transition to steel, formed by alloying iron with carbon (at first from coal furnaces) was all quality. Steel is stronger and harder than bronze or iron, and can hold an edge much better. The steel was made around the 13th century BCE. So why didn’t it eclipse bronze and iron at that time? Because it was difficult to make, and the technology is complex. It requires hot furnaces, and precisely controlling the amount and distribution of carbon. It was therefore difficult to mass produce. Mass production of high quality steel likely started in China in the third century ACE. That’s when the steel age really took off.

The story is a good reflection of the fact that technological change is not always about superior technology, although sometimes it is. There are many considerations that can affect which technologies predominate – cost, convenience, aesthetics, and even culture. Also, many technologies tend to exist side-by-side for a long time. The bronze market is worth about 10 billion dollars today and continues to grow. We produce more bronze now than we did in the bronze age.