32°33′02″N 35°21′25″E / 32.5506°N 35.3569°E / 32.5506; 35.3569

Ma'ayan Harod (Hebrew: מעיין חרוד, lit. 'Harod's spring') or Ain Jalut (Arabic: عين جالوت ‘ayn Jālūt, or عين جالود ‘ayn Jālūd, and Hebrew: גילות, romanized: ain djeluth) is an all-year spring in the Harod Valley (the easternmost part of the Jezreel Valley) on the northwest corner of Mount Gilboa, that was the location of the 13th-century Battle of Ain Jalut. This was a major turning point in world history that saw the Mamluks inflict the first of two defeats on the Mongols that ultimately halted their invasion of the Levant and Egypt.

The traditional name of Ain Jalut has been used since the 12th century and is commonly believed to mean "Spring of Goliath". Alternative etymologies have suggested that it might be derived from the name Gilead, potentially an archaic name for Mount Gilboa. Other names given to the site include "En Harod" or "Ein Harod", a biblical place name that was associated with Ain Jalut in the 19th century; subsequent scholarship, specifically the work of Israel Finkelstein and Oded Lipschits, has refuted this connection. Other associations have also been suggested, including in the 1841 Biblical Researches in Palestine, which linked it to the "spring in Jezreel" where Saul pitched his tent before his final battle, but this was rejected in 1847 and has gained little traction since. The spring is still sometimes known as the "Fountain of Jezreel", as well as "Gideon's Fountain".

According to the medieval chronicler Baha ad-Din ibn Shaddad, there was a prosperous village at the site in the Middle Ages. It was captured by the Crusaders and retaken by Saladin in 1183 CE (579 AH). A later Palestinian village was also established in the area in the late 19th century. In the 1920s, the Zionist activist Yehoshua Hankin purchased the surrounding area as part of the Sursock Purchases through the Palestine Land Development Company, and founded a kibbutz, which he called Ein Harod, near the spring. The site is today incorporated into the Ma'ayan Harod National Park, administered by the Israel Nature and Parks Authority.

The spring is located in the Harod Valley, which is the eastern part of the Jezreel Valley. While the Jezreel Valley is drained via the Kishon River to the Mediterranean Sea, the Harod Valley is drained through the Harod Stream ("Wadi Jalud" in Arabic) to the Jordan River. It is the largest of the springs emerging on the northern slopes of Mount Gilboa. The source of the spring as well as other springs in the Beit She'an Valley to the east, comes from fresh rainwater that percolate into the limestone hills of Samaria and collect in an underground water reservoir beneath the areas of the Palestinian cities of Nablus and Jenin. The water emerges from the hills as they incline north towards the valleys. At this valley the waters emerge from a natural cave known as "Gideon's Cave". The spring's discharge rate is about 360 cubic meters per hour. According to the PEF's Survey of Western Palestine in 1882, Victor Guérin stated that the rock from which the fountain springs has been artificially hollowed into a cavern.

The spring is first recorded as Ain Jalut in the 12th century by Baha ad-Din ibn Shaddad in his biography of Saladin. In that work, the name is presumed to mean "Goliath's spring", alluding to the tale of David and Goliath, with "Jalut" presumed to be an Arabization of "Goliath". This follows a longstanding tradition of narration in relation to the spring. An anonymous Christian traveler from Burdigala mentioned in the year 333/334, a place near the city of Jezreel where biblical David killed Goliath. Kurdish-Jewish folklore similarly places the location of the battle as the "fields of Megiddo" in the Jezreel Valley.

In the 14th century, the Jewish geographer Ishtori Haparchi identified Ain Jalut with the biblical "Spring which is in Jezreel", as well as where the Israelite king Saul prepared his army before the Battle of Gilboa, in which he and his son were ultimately killed. Haparchi dismissed the connection of the spring to Goliath, suggesting that the biblical battle took place between Sokho and Azekah, in Judea, not the Jezreel Valley.

In the 19th century, Arthur Penrhyn Stanley, in his 1856 book Sinai and Palestine, similarly associated Ain Jalut with the "Spring of Jezreel", and also suggested that this could be the same site as En Harod, a place mentioned in the story of Gideon's battle with the Midianites. The name "Harod" translates literally as the "spring of trembling (or anxiety)", a toponym thought to have been used "as a literary illusion to the fear and anxiety of the warriors" ahead of the battle. Stanley noted that the then modern name, "Ain Jahlood" or "Spring of Goliath" may have originated, as observed by Carl Ritter in his 1866 geography of Palestine, from a confused recollection of the earlier stories, but "more probably arose from a false tradition in the 6th century". He separately noted the suggestion by Rabbi Joseph Schwarz, in his 1850 Descriptive Geography of Palestine, that the name "Jalud" could instead be derived from the name "Gilead". Schwarz suggested that this might reminisce an older name for Mount Gilboa, and thus explain the cry of Gideon ahead of his battle: "Whoever is fearful and afraid, let him return, and depart early from Mount Gilead." Schwarz alternatively explains "Mount Gilead" as a "general phrase for the whole tribe" of Manasseh. George Adam Smith, writing in 1920, also noted the similarity of "Jalud" with "Gilead".