How did ancient people learn foreign languages?

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How did ancient people learn foreign languages?
Metatron's Academy | 9 Sept. 2025
https://www.youtube.com/watch?v=Se2dSupqsaw

haec domus - ho oikos
huius domus - tou oikou
huic domui - to oiko
hanc domum - ton oikon
o domus - o oike
ex hac domu - ek tou oikou
hac domu - to oiko

2:32 I just gave an example of formal class room instructions of Latin speakers in Greek and of Greek speakers in Latin.

Such school books have been found.

10:56 Do you know what a Liber Catonicus is?

A beginners' book in Latin, basically the Disticha Catonis and some similarily simple things.

Used both for speakers of Late Latin / Early Romance to acquire literary Latin, and for speakers of Germanic languages to acquire it too, the one as a register, the other as a language.

It has been in use from the time of St. Ambrose roughly to the time of Benjamin Franklin.