Thessaloniki ( Greek : Θεσσαλονίκη , IPA :  [θesaloˈniki] ), Thessalonica , or Salonica is the second-largest city in Greece and the capital of Macedonia , the nation's largest region . It is honorarily called the Συμπρωτεύουσα Symprotevousa (lit. co-capital) of Greece, as it was once called the συμβασιλεύουσα symbasilevousa