To those who knew him, Khaled al-Asaad was as much a part of the city of Palmyra as the ancient antiquities he died seeking to protect.

“The way he’d tell you the stories about Palmyra, you’d feel his passion for the city,” said historian Rim Turkmani, a close friend of al-Asaad and his family. “He had very profound knowledge, he spoke Aramaic, he could read the Palmyran Aramaic and read every inscription and tell you the story behind it.”

The 81-year-old Syrian historian was reportedly killed this week by ISIS militants occupying the ancient historical site, where he was the Director of Antiquities since 1963.