Actually this site is not a holy Muslim site, it's a holy Zoroastrian site.
Iranians were Zoroastrian for hundreds of years before the invasion of Islam from the west from Arabia.
At least. Cyrus the Great captured Susa in 538 BC, and moved the capital of his empire there. The Muslims didn't show up until 639 AD.
So Susa was under Zoroastrianism for 1176 years.