Tartaria refers to the mostly uninhabited eastern part of Russia. Go look at an old map, it was the eastern part of imperial Russia. And the dark ages refers to a time hundreds of years earlier. The fall of the Roman Empire onwards, it's called the dark ages because Europe regressed into warlordism and monarchism. I think it lasted like 600 years. But the rest of the world was still doing their thing, the Arabs and Chinese made a lot of scientific discoveries during the European dark ages.

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.