The Ninth Legion, "the" Lost Legion etc. Made famous by the 1954 historical novel "The Eagle of the Ninth" by Rosemary Sutcliff and a film adaptation in 2011 called "The Eagle". The final fate of the Ninth is uncertain, and the current debate seems stalled due to a lack of definitive evidence. I will attempt to give a survey and a sketch of the Ninth, before telling you why they interest me so much.
Roman legions were recorded in official lists, and there is usually (there is one very important exception that we will get to) a fair bit of supporting evidence of their movements. This could be official documentation, triangulated contemporary accounts, or physical evidence. Legions would stamp the clay roof tiles they made for their camps and forts, for example.
Another important couple of points to note is that the makeup of legions changed over time. When the Ninth disappears from the record, around the end of the 2nd Century AD, a full legion consisted of around 5,200 legionnaries, plus auxiliaries and cavalry if attached. Later legions were smaller. The Ninth is likely to have been anywhere from around 3,000 to 5,000 legionnaries. However, there's another important point to bear in mind, the vexillatio or "detachment" system, whereby elements of legions could be detached and sent as a task force for a specific role and operation. This was a logical choice, but during the 3rd Century legions became divided and mixed. This led to organisational problems within the military (and later reform) and also problems for later historians trying to track units. This confusion is relevant to piecing together (or not) the story of the Ninth.
We know the Ninth moved around a lot during its roughly 200 year history. It fought in Italy, Gaul Spain. After Spain, where they were given their epithet "Hispana", in Britain they suffered at least one defeat but the legion was not annihilated. We know this because they are recorded as being ordered to engage the Brigantes in Northern England subsequently. Elements of the Ninth were later recorded in modern day Germany and Scotland. By the end of the 2nd Century AD, Legio IX Hispana no longer appears in official lists of Roman Legions (but may still have existed in detachments). Marcus Aurelius didn't list the Ninth. Some historians claim scattered reference to them being annihilated before then, but this is not conclusive, to my knowledge at least. The last uncontroversial evidence of the existence of the Ninth is a stone record tablet putting them in York in 107-108AD, after Germany and Scotland.
Remember the important exception to legions being recorded? If they suffered a major defeat, to the extent that they dishonoured Rome, all mention of the legion would be erased, and their numbers would not be used in the future (almost always). After the rout at the Battle of the Teutoburg Forest, the XVII and XIX legions were officially disbanded, erased from public memory, and never raised again. This didn't quite happen with the Ninth though, because their name "Hispana" would have been literally erased wherever it appeared. Did they suffer a defeat that led to them being ignominiously partially erased? Were they detached to the point of being subsumed in other legions? We don't know, but it is definitely strange. Maybe it follows that something strange happened to them...
So, there's my survey of the mystery of the Ninth. So what? In another writeup I mentioned that I started researching a story set in Manchester about a monster that stalks the land and eats people. There was a Roman camp in Manchester, and in my story the monster enters the camp one night, and kills all 500 auxiliary soldier who would have been stationed there. The monster eats his fill and retreats to a deep cellar to sleep it off. The monster lives under the camp for a month, excavates a tunnel and a grendel-cave to be a monster in until it gets hungry again. When it does, around a month later, it wakes from its stupor to find an entire legion has been sent to hastily rebuild and occupy the fort...precipitating a second orgy of violence of much greater proportions.
Very well, the story demands that I find a legion occupying Britain at roughly the right time. Enter, Legio IX Hispana sent from York , to reinforce and subdue Manchester. Exit, Legio IX Hispana, devoured by a monster, and struck from history, leaving only a mystery for my imagination.