March 4 (Reuters) - Rebuilding is due to start on March 9 at the Palestinian refugee camp of Nahr al-Bared, razed in 2007 during battles between the Lebanese army and Islamist militants.

Here are some facts about Palestinian refugees in Lebanon:

* HOW DID THEY GET THERE?

Half the Arabs of Palestine were driven from their homes in 1948 when Israel was created. Descendants of those 770,000 refugees form the bulk of the 4.3 million now cared for by the U.N. Relief and Works Agency (UNRWA), many in slum-like camps in Lebanon, Syria, Jordan, the West Bank and the Gaza Strip.

* HOW MANY ARE THERE?

UNRWA counts more than 400,000 registered refugees in Lebanon, making them roughly 10 percent of the country's population, but migration may have reduced that number. More than half the refugees live in 12 camps, including Nahr al-Bared in north Lebanon, which was home to about 30,000.

* WHAT ARE CAMPS LIKE?

Overcrowded, squalid and often insanitary, a growing refugee population is crammed into the original camp perimeters. Lebanon long hampered improvements by banning building materials from the camps. It barred refugees from about 70 job categories until 2005, when the Labour Ministry cut the number to 20.

* WHY IS LEBANON SO WARY OF PALESTINIANS?

Lebanon has traditionally feared the presence of mainly Sunni Muslim refugees would upset its own delicate sectarian balance. Palestinian guerrilla activities helped destabilise the country as it slid into its 1975-90 civil war. Lebanon's curbs on refugees are designed to deter their permanent settlement.

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