Sentence:  5. To the Romans <WSD>Thulé</WSD>, variously identified as Iceland or Mainland in the Shetland Isles, marked the extreme northern limit of the known world, just as India here stands for the farthest east. 
Meaning of the word marked with <WSD> tags:  The semi-legendary island of classical antiquity considered to represent the northernmost location in the inhabited world (the Ecumene).