The first Marathon Peace March took place in Greece in 1963 despite a ban from the authorities at the time.
The current march started in Greece's Attic Peninsula at 8 a.m. local time [05:00 GMT], the correspondent reported.
"We are sending a signal to fight against the war and Greece’s involvement in it," the organizers of the march said in a statement.
Several hundreds of people are currently marching, however, the number of demonstrators is expected to increase later in the day, the correspondent reported.
The march’s slogans are "No participation in the NATO-US-EU plans," "Close the death bases in Greece" and "We stand for solidarity with the Palestinian people."
Many other anti-imperialist events are expected to take place all over Greece during the day, the correspondent reported.