The siege of Jerusalem in 70 CE was the decisive event of the First Jewish Revolt against the Roman Empire (66–73 CE). Roman forces led by Titus besieged the Jewish capital, the revolt's main stronghold. After months of fighting, they breached the defenses, destroyed the Second Temple, and razed the city, killing, enslaving, or displacing much of its population. The city's fall marked the effective end of the revolt and had far-reaching political, religious, and cultural consequences.

In winter 69/70 CE, after a succession war in Rome, the campaign in Judaea resumed as Titus led at least 48,000 troops—including four legions and auxiliary forces—back into the province. By spring, this army had encircled Jerusalem, whose population had surged with refugees and Passover pilgrims. Inside the city, rival factions led by John of Gischala, Simon bar Giora and Eleazar ben Simon fought each other, destroying food supplies and weakening defenses. Although the factions eventually united and mounted fierce resistance, Roman forces breached the city walls and pushed the defenders into the temple precincts.

In the summer month of Av (July/August), the Romans finally captured the Temple Mount and destroyed the Second Temple—an event mourned annually in Judaism on Tisha B'Av. The rest of Jerusalem fell soon after, with tens of thousands killed, enslaved, or executed. The Romans systematically razed the city, leaving only three towers of the Herodian citadel and sections of the wall to showcase its former greatness. A year later, Vespasian and Titus celebrated their victory with a triumph in Rome, parading temple spoils—including the menorah—alongside hundreds of captives. Monuments such as the Arch of Titus were erected to commemorate the victory.

The destruction of Jerusalem and its temple marked a turning point in Jewish history. With sacrificial worship no longer possible, Judaism underwent a transformation, giving rise to Rabbinic Judaism, centered on Torah study, acts of loving-kindness and synagogue prayer. The city's fall also contributed to the growing separation between early Christianity and Judaism. After the war, Legio X Fretensis established a permanent garrison on the ruins. Inspired by Jerusalem's earlier restoration after its destruction in 587/586 BCE, many Jews anticipated the city's rebuilding. In 130 CE, Emperor Hadrian re-founded it as Aelia Capitolina, a Roman colony dedicated to Jupiter, dashing Jewish hopes for a restored temple and paving the way for another major Jewish rebellion—the Bar Kokhba revolt.

On the eve of the revolt, Jerusalem was a thriving metropolis and the spiritual and political center of the Jewish people in both Judaea and the diaspora. By then, the city had reached its greatest extent, covering about 450 acres (1,800 dunams)—nearly twice the size of today's Old City—and housing tens of thousands of residents. Its renown spread throughout the Roman world. Roman author Pliny the Elder called it "by far the most famous city of the East", while the historian Tacitus described it as "the capital of the Jews", with a temple of "enormous reaches". The city was divided into several districts: the Lower City, a densely populated area; the Upper City, a wealthy quarter inhabited by the city's elite, including priestly families; and the Temple Mount, the religious and political heart of Jerusalem. Its core was the Second Temple, a structure central to Jewish religious and national identity. King Herod, who ruled Judaea between 37 and 4 BCE, greatly expanded and renovated the Temple, transforming it into one of the largest sanctuaries of the ancient world. The temple complex also served as a center of political activity, hosting popular assemblies and judicial bodies, and functioned as one of the city's largest marketplaces. An obligatory half-shekel tax was collected annually from Jewish adults to support the Temple. During Judaism's Three Pilgrimage Festivals, tens of thousands of visitors from both Judaea and abroad traveled to Jerusalem to participate in temple rituals. This regular influx of pilgrims contributed significantly to the city's prominence and prosperity.

Jerusalem's strategic location, flanked by the Kidron Valley to the east and the Hinnom Valley to the south, provided natural barriers that made direct assaults difficult. These natural defenses were reinforced by a series of fortification walls, constructed over the city's long history. The "First Wall", built in the second century BCE by the Hasmonean kings on the foundations of an earlier wall from the time of the kings of Judah, enclosed both the lower and upper city, forming the core of Jerusalem. As the city expanded, the "Second Wall" was built further north to protect new neighborhoods and commercial areas. In the early 40s CE, continued growth prompted the construction of the "Third Wall", initiated by King Herod Agrippa to enclose the northern suburb of Bezetha. Its construction was halted by Emperor Claudius, either due to fears of Jewish rebellion or Agrippa's death. It was eventually completed in haste at the outbreak of the revolt.

The city also featured several fortified structures. At the northwestern corner of the Temple Mount stood the Antonia Fortress, an important military stronghold and palace that overlooked the temple complex. In the western part of the upper city, north of Herod's Palace, stood another fortified complex—now the site of the Tower of David—enclosed by walls and protected by three towers: Phasael, Hippicus, and Mariamne.

Jerusalem's ability to withstand a siege was limited by its reliance on imported food from Judea, Samaria, Galilee, and beyond, as local agriculture could not sustain the population, though the city did maintain food reserves. Its water supply depended on large pools that collected rainwater runoff and channels directing water from sources like the Gihon Spring. Additionally, an aqueduct system brought water from the vicinity of Bethlehem and further south. During the war, the arrival of refugees and insurgents increased the city's vulnerability to famine.