Arsamosata (Armenian: Արշամաշատ, Aršamašat; Ancient Greek: Ἀρσαμόσατα) was a city in Armenian Sophene near the Euphrates. It was founded by King Arsames I of the Orontid Dynasty in the 3rd century BC. It was left and destroyed in the 1st century BC. In the Middle Ages it was called Ashmushat. In Roman and Byzantine times, it bore the names Armosota (Ἀρμόσοτα) and Arsamosota (Ἀρσαμόσοτα).
The conjectured location of the city is somewhere between Kharput (Xarberd) and Palu (Balu). It has also been identified as the abandoned settlement site known as Haraba, located some 60 km east of Elazig, which is where modern scholars locate it.
Much of that site now lies submerged under the waters of the Keban dam. It is not to be confused with Samosata.