Greece has officially taken over the rotating six-month presidency of the European Union amid tightened security in the capital ahead of ceremonies.
Riot police were deployed and roads closed in Athens as protests were banned in the city center.
European Commission President Jose Manuel Barroso and European Council President Herman Van Rompuy are in Athens for the events.
Greatly indebted Greece has been receiving massive billion-dollar loans from the EU and the International Monetary Fund since 2010 in exchange for implementing austerity measures.
Many Greeks are angry at EU officials for imposing what they see as harsh conditions on their daily lives.
The EU announced on January 8 that eurozone unemployment remained at a record 12.1 percent in November.
Greece has the highest jobless rate in the eurozone at 27.4 percent, while Austria has the lowest at 4.8 percent.
Based on reporting by AP, Reuters, and AFP