What is "takht-i-bahi"

Takht-i-Bhai (also spelled Takht Bahi, Takht Bhai or Takh Bay) is a Parthian archaeological site in Mardan, Khyber-Pakhtunkhwa, Pakistan. It was first a Zoroastrian complex which, after the later arrival of Buddhism, was then converted into a Buddhist monastic complex. It is dated to the 1st century BCE. The complex is regarded by archaeologists as being particularly representative of the architecture of Buddhist monastic centers from its era. It was listed as a UNESCO World Heritage Site in 1980.