Thousands took part in the three days of protests in Athens and Thessaloniki to mark the one year anniversary of the death of 15-year-old Alexis Grigoropoulos.
Officers detained some 850 people on Saturday, Sunday and Monday before and during protests and 147 were arrested in protests across Greece.
Most were released without charges.
In Athens, thirty one are to face a prosecutor charged with hooliganism, destruction of property and an attack on Athens University’s rector, Christos Kittas, who was admitted to the hospital in the aftermath of the assault.
The Greek Minister for Public Safety Michalis Chrysochoidis defended the police’s recent tactic of detaining dozens of people as a precautionary measure.
The police have been criticised for what were deemed to be heavy-handed tactics, with some lawyers even expressing doubt about the legality of these pre-emptive detentions.
Chrysochoidis said that “targeted” detentions were a necessary part of the police operation to limit serious incidents of violence in central Athens.
Rioters who used the University of Athens and the Athens Law School as their bases, clashed with thousands of police who had been deployed in the city centre to ensure that the anniversary of the killing of Alexis Grigoropoulos passed as peacefully as possible.
However, following a calm protest by thousands of people on Sunday, scenes reminiscent of those that followed Grigoropoulos’s death last year began to play out on the capital’s streets as rioters threw rocks, burned dumpsters and damaged a dozen stores.
Police reacted by firing tear gas and detaining almost 150 people.
Four citizens and 16 police officers were injured during the clashes. In one of the worst incidents, two policemen were dragged off their motorcycles and beaten over the head with metal chains.
They were taken to the hospital with non-life-threatening injuries.
The rector of the University of Athens, Christos Kittas, was also admitted to the hospital after rioters stormed into his office. Kittas was struck on the head and was taken to the Ippocrateio Hospital, where doctors placed him in intensive care, saying that he had suffered a mild heart attack.
The gates of Athens University had been locked to prevent the premises being used by rioters. A prosecutor yesterday launched an investigation into how they managed to force their way in. Police made a pre-emptive raid on an anarchist hangout in Keratsini near Piraeus on Saturday night where they arrested 22 people.