Saudi Arabia's King Abdullah and Syrian President Bashar al-Assad visit Lebanon on Friday to try to avert a crisis over a tribunal that may indict Hezbollah members in the 2005 assassination of Lebanese statesman Rafik al-Hariri.
Here are questions and answers on Syria's interests in Lebanon, even after it withdrew troops following Hariri's killing, which many Lebanese politicians blamed on Damascus.
WHAT IS THE STATUS OF SYRIAN-LEBANESE RELATIONS?
* Since it was forced to end its 29-year military presence in Lebanon, Syria has been gradually restoring its influence.
* Shortly after becoming prime minister, Saad al-Hariri -- son of the slain billionaire and former premier -- visited Assad in December 2009, ending nearly five years of mutual animosity.
* Since then, Hariri has been to Damascus three more times and Lebanese President Michel Suleiman has also visited.
WHAT HAPPENED TO THE ANTI-SYRIAN ALLIANCE?
* Hariri has toned down his anti-Syrian rhetoric and his government, which includes pro-Syrian and Hezbollah ministers, has pledged to have good relations with Damascus.
* A once-fierce critic of Syria, Druze leader Walid Jumblatt left the anti-Syrian coalition known as "March 14" earlier this year and visited Damascus after mediation by Hezbollah.
* Syria's rapprochement with regional Sunni Muslim power Saudi Arabia, which backs Hariri, has echoed positively in Lebanon. The thaw in Syrian-Saudi ties helped Hariri form a national unity government after defeating the pro-Syrian Shi'ite Hezbollah movement and its allies in a 2009 election.
* Last year Abdullah made his first visit to Damascus since the 2005 assassination of Hariri, a dual Saudi-Lebanese citizen.
* Hariri used to declare that the international tribunal investigating the murder of his father would bring the Syrians to justice. He now says he will accept the tribunal's findings.
WHAT IS THE IMPACT OF THE HARIRI INVESTIGATION?
* United Nations investigators initially implicated senior Lebanese and Syrian security officers in Hariri's killing. Damascus denies any involvement.
* Four pro-Syrian Lebanese generals were held for four years without charge over Hariri's killing. They were released last year after the international tribunal established to try suspects in the case said it lacked evidence to indict them.
* After years of focus on Syria's role, attention has turned to a possible link with Hezbollah. The group's leader, Sayyed Hassan Nasrallah, said this month he was told by Hariri that the tribunal would indict Hezbollah members, not Syrian officials.
* Nasrallah's condemnation of the tribunal as "an Israeli project" drove up tensions in Lebanon. Any indictment of a Hezbollah member could destabilize the unity government.
* Hariri and Suleiman have advocated calm in an effort to avoid a repeat of the divisions that led to violence in 2008.
HOW HAVE DIPLOMATIC, TRADE RELATIONS DEVELOPED?
* Syria and Lebanon opened embassies and appointed ambassadors in each other's capitals in the last two years, the first time they have had formal diplomatic ties since Britain and France carved them out of the old Ottoman Empire in 1920.
* A lavish ceremony marked the first anniversary of the Syrian ambassador's installation in Beirut.
* Economic cooperation accords were signed during Hariri's last visit to Damascus, but border demarcation issues, which Beirut see as central to its sovereignty, were not resolved.
* Trade has slowed in recent years, partly due to political tensions, but Lebanon remains a banking center for neighboring Syria and many Syrian laborers work in Lebanon.
WHY DOES SYRIA BACK HEZBOLLAH?
* Syria, seeking the return of the Israeli-occupied Golan Heights, can project regional power via its influence in Lebanon, especially its ties with the Iranian-backed Hezbollah.
* Syria, which has lost several wars with Israel, relies on Hezbollah guerrillas to thwart Israel's ambitions in Lebanon and fight a proxy conflict with the Jewish state. Turkish-mediated peace talks between Syria and Israel collapsed in late 2008.
* Syria has been accused of re-arming Hezbollah since the Shi'ite fighters held off Israel in a 2006 war in Lebanon.
(Compiled by Khaled Yacoub Oweis, Yara Bayoumy and David Cutler; editing by Alistair Lyon)