Given the task definition and input, reply with output. In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.

In classical antiquity , Illyria ( ; , " Illyri a " or , " Illyri s " ; , see also : " Illyricum " ) was a region in the western part of the Balkan Peninsula inhabited by numerous tribes of people collectively known as the Illyrians .
Illyria was an ancient region in the western part of today 's Balkan Peninsula .