What is the relationship between Syriza and Athens in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

A September 20 victory for Syriza would deliver "a key message for Europe", Tsipras told his closing rally in Athens on Friday, referring to the refugee crisis and to EU economic woes.

Answer: headquarters_location