I have no idea on the literacy rate in the Middle Ages, but estimates for the Roman empire range between ten and twenty percent. That's actually not that impressive. I'm also not sure how important it was to be literate when signing up for the roman army or if there was any training offered after you joined up. You spent 25 years there after all before getting the honesta missio and a patch of land.
I guess the Middle Ages being different is down to many factors. At least in Western Europe the absence of solid social and political structures. Your immediate superiors were feudal lords, often only in posession of a couple of villages and you hardly ventured beyond that reign. And then there's the monopoly of the church when it came to knowledge and education. Things look of course differently in the East. Constantinople lasted till 1453, and we have a number of reports on how travellers from there looked down on the Western realms.
I guess the Middle Ages being different is down to many factors. At least in Western Europe the absence of solid social and political structures. Your immediate superiors were feudal lords, often only in posession of a couple of villages and you hardly ventured beyond that reign. And then there's the monopoly of the church when it came to knowledge and education. Things look of course differently in the East. Constantinople lasted till 1453, and we have a number of reports on how travellers from there looked down on the Western realms.