The Archbishop of York has moved into a tent in York Minster as part of an act of "public witness" to encourage peace in the Middle East.
Dr John Sentamu will live on a liquid diet while he camps inside the Minster for seven days, to highlight the plight of people caught up in the conflict.
He has given up a family holiday in Salzburg, Austria, to sleep rough and fast while praying for peace.
To launch the vigil on Sunday he publicly had his head shaved.
Cathedral cleric Canon Glynn Webster used a pair of electric trimmers for the archbishop's haircut, carried out on the altar.
Dr Sentamu said he hoped people from all faiths would join him in praying for peace.
He will lead prayer every hour for seven days, with his fast ending at 1000 BST next Sunday.
He said his actions mirrored those of countless numbers of people caught up in the conflict between Israel and Lebanon, who were having to sleep rough and without proper food.
More than 1,000 Lebanese and more than 120 Israelis have been killed in the conflict since Hezbollah militants captured two Israeli soldiers on 12 July in a cross-border raid.
Dr Sentamu said: "This act is a rallying call to people of all faiths and none, to encourage them to feel that there is something that can be done.
"The UN has a role, diplomacy has a role and our government has a role to play in bringing this conflict to an end.
"But we as people also have a role to play in showing our common humanity with all those who are suffering."
Dr Sentamu is also urging people to give up a meal and donate the money to charities that are working in the crisis region.
United Nations secretary general Kofi Annan has announced that a ceasefire between Hezbollah and Israel will come into effect at 0600 BST on Monday.
However, Israel is likely to continue operations in Lebanon on Sunday in an effort to clear the south of Hezbollah.
Hezbollah's leader has said his group would abide by the ceasefire plan, but Sheikh Hassan Nasrallah said on TV that Hezbollah would continue fighting as long as Israeli soldiers remained in Lebanon.