Tartaria refers to eastern Russia and inland Asia
It was essentially the "wild land" that Europeans didnt know about.
That's it, and the dark ages were hundreds of years prior, known as the dark ages because Europe regressed after the fall of Rome into warlordism and monarchism.
The history of the dark ages is pretty well known, bunch of warring kingdoms in Europe.
Meanwhile the Arabs and Chinese were still doing their thing making scientific discoveries and progressing their societies.
