Excavations began in the 1930s, conducted by a French mission headed by L. Delaporte. By investigating the upper part of the mound, Delaporte unearthed the remains of remarkable Iron Age buildings, among which the so-called neo-Assyrian palace (7th century BC) and the well-known Lions' Gate (10-9th centuries BC) (Delaporte 1939; 1940). The gate was flanked on either side by two lions statues carved from stone blocks with high relief bodies and round heads, which probably gave the name to the site (Arslan Tepe, namely, "Lions' Hill"), and had walls lined with stone slabs decorated with bas-reliefs, whose iconography and style were typical of the neo-Hittite kingdoms art (Delaporte 1940). Inside the gate, was a great royal statue that had been felled and probably intentionally concealed. The Second World War put an end to the work of the Delaporte expedition and after a short and rather fruitless resumption of excavations in 1949-51 by C. Schaeffer, the French activity in the site came to an end.
In 1961 a new Italian archaeological project began at Arslantepe, originally under P. Meriggi and S. Puglisi and soon after under the latter alone (Puglisi, Meriggi 1964), which is still being operating in the site, and has since become one of the major archaeological projects of Rome's La Sapienza University. After Puglisi, the excavations were taken over by Alba Palmieri and are now continuing under the author’s direction.
The Italian mission started investigating in the same NE zone where the French had previously worked, identifying the stratigraphic sequence along the northern edge of the mound. There, a number of building levels dating back to the 1st and 2nd millennia BC – Neo-Hittite (Iron Age), Imperial Hittite (Late Bronze II) and Early Hittite (Late Bronze I) periods – (Pecorella 1975; Palmieri 1978), have been brought to light above unsubstantial Early Bronze layers with scanty architectural remains and a series of seven building levels with domestic structures from Late Chalcolithic 3-4, built on the virgin soil (Palmieri 1978: 315-330). The sequence ended with the remains of a late Roman occupation (Equini Schneider 1970).
In the last 35 years the researches have focused on the prehistoric and proto-historic levels of Arslantepe, by operating in the W and SW zones of the mound, where the earliest settlements made up the original nucleus of the tell. There, a long and detailed sequence of Late Chalcolithic, Early Bronze, and Middle Bronze levels, from the end of the fifth to the beginning of the second millennium cal BC, has been investigated over vast areas, supported by about one hundred C14 dates (Di Nocera 2000 a and b; Frangipane 1993c; 1996; Palmieri 1981).
Only recently, in 2008, excavations in the NE zone were resumed to once again investigate, by using modern research methodologies, the important phases in the late history of the site, between the Hittite "conquest" of the region, the subsequent dismemberment of the imperial system, and the formation of the neo-Hittite kingdom of Malatya.