More about the riots
CNN has posted a very in-depth article here detailing the history of Greece, and a further explanation of unrest here. I highly recommend you read it to know better how to pray for this nation.
We seem to have arrived here at an interesting time in Greece’s history. We have seen our share of protests, and we have been affected by many strikes in our 15 months here. Through it all we have continued to see that Greece is in a state of transition, looking for hope somewhere. We find it tragic that the gospel seems so obscured here, despite the heavy-handed presence of the church here.

image via The New York Times
Tonight in our neighborhood, I [Paul] heard some shouts and decided to take off on my scooter to investigate. I was treated to a peaceful demonstration by leftist students marching from Polytechniou University in our neighborhood toward the center of Athens. They were peaceful, only chanting slogans of solidarity and statements of dissent. They passed the local police station peacefully, which was a concern of mine since the police are the object of their anger right now. There is tension in the air here in Athens, and we ask you to be praying for the nation of Greece.
Catherine and I took time today to pray that God would restore the hope of Greeks through Christ, that He would grant wisdom to the government in guiding their nation past this crisis, and that He would show His grace in public acts of forgiveness and peace - rather than anger and violence.
I want to reiterate to you our safety here. We are being careful and watchful, but we sense no real danger here in our neighborhood. Student protests are generally peaceful in our neighborhood. Most violence occurs in the center, and is easy to avoid. Thanks for praying with us.
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I have been praying for you. I am glad you are keeping us updated on your website. I will add your prayer requests to my prayers. Tua amica, Magistra