The hill which takes the form of a horst originated in the Miocene epoch (23–25 million years ago) and consists of Jurassic limestone dating back to the Oxfordian age (155–161 million years ago). This limestone is strongly karsted and abounds in caves (e.g. the Dragon's Den—Smocza Jama). This possibly explains why the hill was originally called "wąwel", meaning ravine in Polish. This ravine once divided the hill. An alternative theory is that the word means 'protrusion from the marshes' which surrounded the hill. However, the most recent theory is that "Wawel" is a regular continuation of the name Babel in the Greek language (the consonant followed by [V/Piotr Makuch, Wawel – starożytny Babel. Rozwiązanie zagadki, "Alma Mater", 2008, nr 104–105, s. 57–61</ref>