Explanation: In the Roman Legions, there were a group of soldiers called immunes who were, well, immune to certain tasks, like guard duty, digging ditches, etc. This was highly valued - fuck digging ditches all day! The most common way to become an immunis was to take up a useful trade the Legion needed - such as carpenters, hunters, field medics - and musicians! The norm was for each immunis to have a trained replacement lined up and ready when they retired or kicked the bucket - but that didn't always work out as planned. One imagines a few tin-ears must've slipped in over the years!