The Cave of Letters (Hebrew: מערת האיגרות, romanized: Marat Ha-Igerot) is a refuge cave in Nahal Hever in the Judean Desert where letters and fragments of papyri from the Roman Empire period were found. Some are related to the Bar Kokhba revolt (circa 131–136 CE), including letters of correspondence between Bar Kokhba and his subordinates. Another notable bundle of papyri, known as the Babatha cache, comprises legal documents of Babatha, a female landowner of the same period.

The cave is located at the head of Nahal Hever in the Judean Desert, about 40 kilometres (25 mi) south of Qumran, 20 km south of Wadi Murabba'at. The site is a few kilometers southwest of En-gedi, approximately 10 kilometers north of Masada, on the western shore of the Dead Sea. The cave has two openings, three halls and some crevices.

The cave was discovered by Bedouin of the Ta'amireh tribe and explored in 1953 and 1955 by inspector of the Israel Department of Antiquities, Yohanan Aharoni. In 1953, after the sale of letters written by Bar-Kokhba found in the caves of Wadi Murabba'at, an expedition was organized to explore these caves. However the expedition first visited Nahal Hever, where the team noticed remnants of a Roman siege camp directly above the Cave of Letters. Another camp was also discovered on the southern side of the ravine.

In the Cave of Letters, archaeologists found Chalcolithic remains from the 4th millennium BCE as well as artifacts from the Roman period. Further exploration of the cave was abandoned because of some boulders obstructing access to other parts of the cave. It was not until 1960, when more documents from the Bar-Kokhba Revolt were sold to scholars in Jordan, that further exploration was approved. On March 23, 1960, four teams set out to explore the caves over a period of two weeks. Yigael Yadin led a team to search the northern side of the ravine at Nahal Hever.

The first finding was of a niche of skulls. Tucked away in a crevice opening were remains of human skeletons, wrapped in textiles and covered in a large mat. One skeleton was covered by a colorful mat and other textiles, while the remains of a child dressed in a tunic were discovered in a leather lined basket. The textiles found were some of the earliest known of the Roman period and were dated around 135. These textiles were of importance in showing the kinds of dyes and the weaving material used. Also of importance was the acquisition of a complete set of clothes worn by Jews of the 1st and 2nd century. Among them were adult-sized mantles, a child's linen tunic, and some un-spun wool dyed purple.

Other finds of archeological significance were samples of Bar Kochba Revolt coinage, inscribed on one side 'Shimeon' and on the other, 'to the Freedom of Jerusalem' (לחרות ירושלם). Some arrows were found at the entrance to the cave, and a basket of bronze vessels and incense shovels. They had been made with Roman images on them, but the faces of the various pagan gods and creatures were defaced (see Aniconism in Judaism).

A tied bundle of documents, the Bar-Kokhba letters, was found in a waterskin, next to what were apparently a woman's belongings: wool, cosmetic tools, beads, a perfume flask and a mirror.

Of fifteen letters, most were written in Aramaic and Hebrew, and two in Greek. Most were addressed from the leader (but not in one handwriting) to his subordinates Yehonathan and Masabala, who sat at En-Gedi. Yadin theorized that Yehonathan and Masabala finally carried their cache to the cave. The letters are linguistically interesting as they include many spelling errors, revealing a spoken Hebrew which parallels in places phenomena from modern colloquial Hebrew despite the two sharing no direct relation.^{[citation needed]}