The oldest surviving art dates back 30,000-33,000 years ago and includes sculptures made from bone, ivory, stone, and antlers. Many of these sculptures are assumed to be fertility figures. Cave paintings from 15,000 years ago often depict animals pierced with arrows, possibly representing hunting rituals. Megalithic structures from 4,000-6,000 years ago, like Stonehenge and Newgrange, had astronomical alignments and were likely used for spiritual ceremonies. Prehistoric peoples transported huge stones by leveraging them onto wooden sledges pulled by large groups of people.