), also known as Thessalonica, Salonika or Salonica, is the second-largest city in Greece and the capital of Greek Macedonia, the administrative region of Central Macedonia and the Decentralized Administration of Macedonia and Thrace.t is an influential city for the northern parts of the country and is the capital of the region of Central Macedonia and the Thessaloniki regional unit. The Ministry of Macedonia and Thrace is also based in Thessaloniki, being that the city is the de facto capital of the Greek region of Macedonia.