Israel laid siege to an 889-year-old castle. Here's why that matters

Israel has captured an 889-year-old castle in southern Lebanon in a mountainous military siege that marked Israeli forces' deepest incursion into the country in 26 years.

The operation at Beaufort Castle, also known locally by its Arabic name Qal'at al-Shaqif, occurred within 10 kilometres of the Israeli border and near the city of Nabatiyeh.

It came after days of fighting and air strikes in nearby villages where Israeli troops fought members of terror organisation Hezbollah.

Israeli Defense Forces soldiers stormed Lebanon's Beaufort Castle during the sunset hours. (Reuters: Supplied/Israel Defense Forces)

The castle's seizure represents a major gain for Israel in the latest Israel-Hezbollah war, which began in early March.

The strategic advance was also conducted amid a nominal ceasefire that has been in place since April 17 and ahead of planned peace talks between Israel and Lebanon in Washington DC this week.

Here is what is known about Beaufort Castle and why Israel set its sights on its capture.

Lebanon's Qal'at al-Shaqif was first built around the year 1137 but has since been expanded, modified and rebuilt by ruling groups through history such as the Ayyubids and the Mamluks, according to UNESCO.

It "commands a strategic position, dominating a landscape that extends across the territories of Lebanon, Syria, and Palestine," the UN agency says.

Beaufort Castle sits atop a mountainous ridge that overlooks parts of southern Lebanon and the Litani River. (Reuters: Amir Cohen)

Built as a Crusader castle on top of previous fortifications, it has also been used by Saladin's Jerusalem army, the Ottomans, the French mandate and the Palestine Liberation Organization (PLO).

The Crusaders named it Beaufort, which is Old French for "beautiful fortress".

In 1982 it was held as a strategic stronghold for the PLO and became the centre of a war that Israel still credits as a military achievement in Lebanon, according to the Israel Defense Forces.

During the Israel-Lebanon war, also known by Israeli forces as the "Operation Peace for Galilee", Israel drove the PLO out of the country and advanced north to attack parts of Beirut, led by then-defence minister and future prime minister Ariel Sharon.

Israeli troops have captured a strategic mountain topped with a Crusader-built castle in southern Lebanon.

In 2000, Israeli forces withdrew from the site and it was later opened to visitors before a large-scale conservation project began to repair and restore it after the significant damage it sustained during the fighting.

In the wake of Israel's renewed figh