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During the later thirteenth century , the ancient Italian city of Viterbo was the site of five papal elections and the residence of seven pope s and their Curia s , and it remains the location of four papal tombs .
 Viterbo
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Viterbo