48860
However , since prehistory , they have also been built and used as burial monuments ; for defense and hunting ; for ceremonial purposes , sometimes relating to astronomy ; to locate buried items , such as caches of food or objects ; and to mark trails , among other purposes .
 prehistory
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 prehistory