The language of classical-helenic-romaic-byzantine Greece deserves a special attention in the philological studies. It is the first known literature language but considered a spoken language as well  like every other spoken one, is believed to have borrowed a large amount of loans from its substratum .

What is a substratum of a language?

The academical definition for it is the following:

In linguistics, a substratum (lat. sub: under + stratum: layer → lower layer) is a language which influences another one while that second language supplants it. The term is also used of substrate interference, i.e. the influence exerted by the substratum language on the supplanting language .

So under-stratum (language) is believed to be a foundation for another language. Read more of this post