The Iron Reavers are one of the more enigmatic leftovers of the Mage Wars, perhaps because, like so many things from the First Chaotic Period, no one is entirely certain why they were made, who made them, or what they were made for. Even the origins of the name itself are unclear.
Much like snowflakes, no two Iron Reavers are the same. Some walk, some fly, some burrow underground. Some are enormous (even the smallest is the size of a building). Some walk on two legs, with arms and a head like a man; others have been sighted with thousands of legs. Many of the larger reavers are described as not even looking like humans: some appear to be floating mountains with tentacles like tree roots.
Stories of creatures like the Iron Reaver date as far back as the Age of Darkness, but many such ancient accounts are not considered credible. Importantly, the so-called "strong" First Chaotic Period sources, such as High Tower and the Bur'Ians, fail to mention the Iron Reavers at all.
The earliest reliable information has the reavers already existing by the mid-to-late First Chaotic Period (the earliest surviving accounts indicate that they were already a problem by then), so best estimates put the creation date somewhere in the early-to-mid.
During the Dynastic Period many more credible sources list numerous sightings, conflicts, and battles with Iron Reavers. The Marcons, in particular, attempted to create a catalogue of all known Iron Reavers, and collected hundreds of accounts. Tens of thousands of marcons died trying to gather information on the reavers.
By the Second Chaotic Period, the general population had gotten a hand on them, and adventurers everywhere managed to kill countless Iron Reavers. Reaver City on the Agras Plain was known since the late Dynastic Period as a tourist attraction, as the city was built on, in, and out of the corpse of a massive Iron Reaver.
Many theories abound concerning the nature and origin of Iron Reavers. They are almost certainly artificial in nature; anything else is speculative.
The Infinite Account is a famous scrap of document (about half a sheet of parchment), part of a cache of documents dating to the early Intermediate Period, and contains one of the most vivid and terrifying accounts of what is believed to be the largest Iron Reaver. It states that the reaver was "the size of a hundred-story mage tower"; which would put its height about 1,000 feet. Mage Towers were never measured in what we typically view as stories in modern buildings: a "story" could be as little as ten inches, or as high as fifteen feet. Based on excavations of contemporary mage towers, many put the size at around a few hundred feet tall (the average tower being 15 to 30 storeys).
However, the source of the document is most important, here. The Marcon Alliance had already begun building towers by that time, and tended to make theirs very tall. If the document is Marconian in origin, the Infinite One may have been two thousand feet tall.