Complex sentence: The Thamud civilisation were famed for their engineering abilities as they used to carve entire buildings out of mountains and some Thamud-made buildings can still be seen in Mada'in Saleh in modern-day Saudi Arabia.
Split into simpler sentences: The Thamud civilisation was famed for their engineering abilities as they used to carve entire buildings out of mountains. Some Thamud-made buildings can still be seen in Mada'in Saleh in modern-day Saudi Arabia.