The protest at the famous landmark was in support of Eta militants
A Basque activist has been seriously hurt in a fall from the Arc de Triomphe during a demonstration in Paris.
Police have arrested the man and seven other activists, who unfurled a banner at the top of the monument, facing the Champs-Elysees.
It is not yet clear why the man, who was abseiling down from a parapet near the top, plunged to the ground.
The banner called on the French and Spanish governments to explain the death of a Basque militant, Jon Anza.
Police and medics went to the activist's aid. He is reported to have broken his ankles and hurt his head, but his injuries are not thought to be life-threatening.
Anza, a militant in the Basque separatist movement Eta, disappeared a year ago and was found dead in March in Toulouse, southern France.
The injured Basque activist was helped by medics at the scene
The banner, referring to the governing parties in Spain and France, said: "PSOE-UMP, what have you done with Jon Anza?"
Another one of the abseiling activists got stuck in scaffolding on the Arc, which is 51m (168ft) high.
Eyewitness Andrew Wong told the BBC that the activist who fell to the ground had been dangling about 3m below the parapet near the top.
Eta, which is classified as a terrorist organisation by the US and the EU, resumed attacks in June 2007 after a truce of 15 months. Spanish police have often been the targets.
France's President Nicolas Sarkozy has said France will rid itself of bases run by Eta. The group is blamed for the deaths of more than 800 people since the late 1960s in its campaign for an independent Basque state.
There have been frequent arrests of Eta suspects in France, often in the south-west.