Masada mesa. Herod's palace was built on the three tiers at north end (right).

Hebrew: "Fortress"

Inaccessible fortress atop a large [1900 x 650 feet] boat-shaped mesa on the Dead Sea's western shore, rising almost 1300 feet above the surface of the sea below. The site was named & first fortified by a Hasmonean ruler named Jonathan [either the youngest brother of Judah Maccabee or more likely Alexander Jannai]. 

Herod left his family there while he went to Rome after Antigonus & his Parthian allies had captured Jerusalem (40 BCE). After securing his kingdom, Herod reinforced the fortifications [with a 13 foot thick wall & 110 towers rising as much as 100 feet above the mesa top] & built a magnificent three level palace on the northeastern face of the the mesa. This palace was an architectural & engineering wonder, featuring the most innovative technology & luxuries of the Augustan era. Huge storehouses & cisterns carved out of the mesa held enough food & water to withstand more than 5 years of siege.

modern walkway connects ruins of Herod's 3 tier palace in cliffs at Masada

After Archelaus was deposed (6 CE), the fort was maintained by a small Roman garrison that was overwhelmed by zealot forces during the Jewish revolt of 66 CE. When the Romans captured Jerusalem (70 CE), Eleazar ben Jaïr---a descendent of Judah of Gamala---led the remnants of the sicarii [assassin faction  of revolutionaries] to Masada, where less than 1000 Jews resisted almost 15,000 soldiers of the 10th Roman legion for 3 years. (The foundations of the Roman camps are still visible from the plateau). According to Josephus [War 7.320-406], when the Romans finally took the fortress (in May 73 CE), they found that all but seven of the defenders had committed suicide rather than surrender. Modern excavations at the site have unearthed a 36' x 45' hall that the zealots had converted into a synagogue similar to the one at Gamala.

Masada synagogue

References: Josephus, Antiquities 14.296, 358-361, 390-400; 15.184. 
                   _____, War 1.237-238, 286-294: 4.399-404; 7.275-406.

For further information about archaeological & historical evidence, see:

• Rousseau, John J. & Rami Arav. Jesus & His World. (Minneapolis: Fortress Press, 1995) pp. 194-198.

Other resources on line:

• The Credibility of Josephus - Shaye Cohen separates probable fact from obvious fabrication in Josephus' account of the fall of Masada [PBS Frontline: from Jesus to Christ].

• Masada: Desert Fortress - Israeli government's illustrated e-guide to Yigael Yadin's excavations.

• Masada - Donald Binder focuses on images of the Masada synagogue (Second Temple Synagogues).

• Masada - high resolution photos posted by Bible Places.

• Masada - entry in Israeli Mosaic: the Unofficial Guide

• Masada - article in Wikipedia's web.