Ištaran was the tutelary god of
Der. His
temple located there was known under the ceremonial
Sumerian name Edimgalkalamma, "House, Great Bond of the Land". A library was attached to it, and it is known the scribes of Der were in contact with those from
Uruk and
Babylon. However, as of 2010, only seven tablets whose
colophons state they originate in Der are known. Oldest attestations of Ištaran are royal inscriptions from the
Early Dynastic period from
Lagash and
Umma, and one of such texts attributed to
Entemena relays how
Mesalim of
Kish at the command of Ištaran demarcated the border between these two states, represented by their gods
Ningirsu and
Shara. It has been proposed that Ištaran was understood as a neutral party, similarly to how
Dagan was portrayed in similar texts from contemporary Syria, and as such as a suitable deity to ask for resolution of such conflicts. Another Early Dynastic ruler,
Lugalzagesi, called himself a "beloved friend of Ištaran".
Theophoric names invoking Ištaran also first appear in sources from the Early Dynastic period. Evidence for the worship of Ishtaran in the
Sargonic period includes a mace head dedicated to him by
Naram-Sin of Akkad, found in
Ur, and theophoric names from
Adab, such as Ur-Ištaran.
Gudea, who reigned after the fall of the Akkadian Empire, in an inscription compared himself to Ištaran, asserting that like him he would declare just judgments not only for Sumerians and Akkadians, but even for "a brute from
Gutium". In the following
Ur III period, king
Shulgi patronized the Edimgalkalamma. A Sumerian text from the third millennium BCE found in Susa, where it was presumably brought in the aftermath of an Elamite raid, also mentions work undertaken in his temple in Der, might predate his dynasty, but the name of the ruler responsible for it is lost. One of Shulgi's daughters bore the name ME-Ištaran (reading of the first element uncertain), as attested in documents from the
Garšana archive, which detail matters related to her estate located there and mention her marriage to a certain Shu-Kabta, a man who was apparently both a physician and a military official. The formula "favorite of Ištaran, beloved of
Inanna" (
migir Ištaran, naram Inanna) was used by the viceroys of Der Ilum-muttabil (also read Anum-muttabil), Nidnuša, and a third holder of this office whose name is not preserved. They reigned during Der's period of independence after the fall of the
Third Dynasty of Ur. In this period the rulers of Der were considered representatives of Ištaran on earth, which is presumed to parallel the development of similar models of rulership in
Eshnunna and
Assur, where the local rulers similarly were believed to act as governors on behalf of
Tishpak and
Ashur, respectively. An inscription of Ilum-Muttabil indicates that he dedicated a new construction project to Ištaran too, but it is unknown if it refers to a temple. Eckhart Frahm notes that it is not impossible repairs of Edimgalkalamma are described in it, though he due to their poor preservation of the text cannot be established with certainty. In a royal inscription preserved on a clay cylinder found in
Ur,
Sin-Iddinam of Larsa recorded that after defeating and taking captive an enemy ruler, Warassa, he entrusted him to Ištaran and released his imprisoned troops, and states that the king declared he took these actions "In order that my name is mentioned in Der in remote (days)". Warassa might have ruled over either Der itself, much like his namesake known from sources contemporary with the reign of
Hammurabi of
Babylon, or nearby
Malgium; the third proposed location he might have hailed from,
Eshnunna, is considered unlikely, as Sin-Iddinam refers to him as
lugal, rather than
ensi2, the typical title of Eshnunnean rulers. An inscription of the
Assyrian king
Ilu-šūma mentions Ištaran and his city in passing. This text is the oldest known reference to cities other than
Assur in Assyrian royal inscriptions. In the
Old Babylonian period, a man bearing the theophoric name Ištaran-nasir was a merchant active in
Carchemish and was in contact with
Zimri-Lim, the king of
Mari, informing him about events such as a festival of
Nubandag and the death of king
Aplahanda. In the
Kassite period, Edimgalkalamma was rebuilt during the reign of one of the two kings bearing the Kurigalzu (
Kurigalzu I or
Kurigalzu II). The 1920 discovery of a text documenting this event contributed towards identifying its findspot, Tell Aqar, as the location of Der. He is also referenced in an inscription from Susa from the reign of one of the Kurigalzua, and possibly in another from Babylon also attributed to one of them. Furthermore, he appears in eleven theophoric names from
Nippur from the Kassite period, with further five invoking "Anu Rabû". He is also one of the few Mesopotamian gods attested in linguistically
Kassite theophoric names, which usually invoked
Kassite deities rather than Mesopotamian ones. Multiple people bearing theophoric names invoking Ištaran (dKA.DI or AN.GAL) are also attested in the documents of the
First Sealand dynasty, and Ran Zadok proposes that these individuals originally came from Der. He is also invoked in the Elamite name Kuk-Ištaran, "protection of Ištaran". An inscription of king
Marduk-nadin-ahhe of the
Second Dynasty of Isin mentions Anu Rabû as the last god in a long sequence of deities, immediately after
Išḫara. In later periods Ištaran was worshiped in the treasury of the Ešarra temple in Assur. Assyrians also intervened a number of times in the religious affairs of Der, and repeatedly carried off and returned the statue of Ištaran in order to ensure the loyalty of local inhabitants. During the reign of
Shamshi-Adad V, statues of the deities of Der, including Ištaran, as well as Šarrat-Deri,
Mār-bīti,
Urkitum,
Saĝkud of Bubê and others, were seized by the Assyrian army which attacked the city, as documented in a letter of this king addressed to the god Ashur. They were later returned by
Adad-nirari III. The city god was however subsequently taken away once more on the orders of
Sennacherib to punish the local population for their earlier support of the Elamite king , who campaigned in Mesopotamia against
Aššur-nādin-šumi, the Assyrian ruler's son and governor of
Babylonia. However, he was once again returned when
Esarhaddon ascended to the throne, which was a part of a broader process of reversal of his predecessor's policy towards southern cities. He also renovated the Edmigalkalamma, which was damaged in an Elamite invasion during the reign of
Enlil-nadin-šumi. Esarhaddon's efforts were subsequently continued by his son
Ashurbanipal, as documented in three texts from
Nineveh. Most likely the work in Der was stretched over the course of multiple years, starting before 652 BCE and concluding at some point between 647 and 645 BCE. A text from Ashurbanipal's reign also mentions Ištaran (under the name
Anu Rabû) as one of the deities who aided this king during a campaign against Elam (653 BCE) alongside Ashur,
Lugal-asal,
Marduk,
Nabu and
Shamash. Ištaran most likely continued to be worshiped in Der until the city was deserted in either the
Seleucid or
Parthian period. While in the past it was assumed that theophoric names invoking him stopped being used after the Kassite period, more recent research shows that scribes from Der still bore such names in the late first millennium BCE. ==Mythology==