Policemen try to put out fire at Exarchia in Athens, Greece, on Dec. 6, 2018. Protests held in several Greek cities on Thursday in the memory of Alexandros Grigoropoulos, a teenager shot dead by a police officer in Athens in 2008, were marred with violent incidents. At least 27 demonstrators in the Greek capital, Thessaloniki in northern Greece and Chania on Crete island were detained and held in custody for participating in clashes with anti-riot police forces and vandalism, according to Greek national news agency AMNA. (Xinhua/Marios Lolos)