Masada occupies the entire top of an isolated mesa near the southwest coast of the Dead Sea. The rhomboid-shaped mountain towers 1,424 feet (434 m) above the level of the Dead Sea. It has a summit area of about 18 acres (7 hectares). Some authorities hold that the site was settled at the time of the First Temple (c. 900 BC), but Masada is renowned for the palaces and fortifications of Herod the Great (reigned 37–4 BC), king of Judaea under the Romans, and for its resistance to the Roman siege in AD 72–73.

The site was first fortified either by Jonathan Maccabeus (d. 143/142 BC) or by Alexander Jannaeus (reigned 103–76 BC), both of the Hasmonean dynasty. Masada was chiefly developed by Herod, who made it a royal citadel. His constructions included two ornate palaces (one of them on three levels), heavy walls, defensive towers, and aqueducts that brought water to cisterns holding nearly 200,000 gallons (750,000 l). After Herod's death (4 BC), Masada was captured by the Romans, but the Zealots (Zealot), a Jewish sect that staunchly opposed domination by Rome, took it by surprise in AD 66. The steep slopes of the mountain made Masada a virtually unassailable fortress.

Following the fall of Jerusalem and the destruction of the Second Temple (AD 70), the Masada garrison—the last remnant of Jewish rule in Palestine—refused to surrender and was besieged by the Roman legion X Fretensis under Flavius Silva. Masada's unequaled defensive site baffled even the Romans' highly developed siegecraft for a time. It took the Roman army of almost 15,000, fighting a defending force of less than 1,000, including women and children, almost two years to subdue the fortress. The besiegers built a sloping ramp of earth and stones to bring their soldiers within reach of the stronghold, which fell only after the Romans created a breach in the defenders' walls. The Zealots, however, preferred death to enslavement, and the conquerors found that the defenders, led by Eleazar ben Jair, had taken their own lives (April 15, AD 73). Only two women and five children—who had hidden in a water conduit—survived to tell the tale. Masada was briefly reoccupied by the Jews in the 2nd century AD and was the site of a Byzantine church in the 5th–6th century. Thereafter, it was abandoned until the 20th century, except for a brief interval during the Crusades; the Arabs called the mountain As-Sabba (“The Accursed”).

A general survey of the ruins was made by Israeli archaeologists in 1955–56, and the entire mountaintop was excavated by Yigael Yadin in 1963–65, assisted by thousands of volunteers from around the world. Descriptions by the Jewish historian Josephus, until then the only detailed source of Masada's history, were found to be highly accurate; the palaces, storehouses, defense works, and Roman camps and siege works were all revealed and cleared, as was the winding trail (the “Snake Path”) on the mesa's northeastern face. A synagogue and ritual bath discovered on Masada are the earliest yet found in Palestine. Among the most interesting discoveries is a group of potsherds inscribed with Hebrew personal names. These may be lots cast by the last defenders to determine who should die first.

In the 20th century Masada became a symbol of Jewish national heroism, and it is now one of Israel's most popular tourist attractions. The difficult ascent of its footpaths is regularly performed by Israeli youth groups, while a cablecar provides tourists with a less rigorous access route. Arkia, Israel's domestic airline, provides regular service to a small airfield on the adjacent Dead Sea plain.