The Treasury of Atreus or Tomb of Agamemnon is a large tholos or beehive tomb on Panagitsa Hill at Mycenae, Greece, constructed during the Bronze Age around 1250 BC. The stone lintel above the doorway weighs 120 tons, with approximate dimensions 8.3 x 5.2 x 1.2m, the largest in the world. The tomb was used for an unknown period. Mentioned by the Roman geographer Pausanias in the 2nd century AD, it was still visible in 1879 when the German archaeologist Heinrich Schliemann discovered the shaft graves under the "agora" in the Acropolis at Mycenae.

The tomb perhaps held the remains of the sovereign who completed the reconstruction of the fortress or one of his successors. The grave is in the style of the other tholoi of Mycenaean Greece, of which there are nine in total around the citadel of Mycenae and many more in the Argolid. However, in its monumental shape and grandeur it is one of the most impressive monuments surviving from the Mycenaean period.

The tomb has probably no relationship with either Atreus or Agamemnon – legendary rulers of Mycenae or Argos in the works of Homer, in the Epic Cycle, and the Oresteia – as archaeologists believe that the Mycenaean sovereign buried there ruled at an earlier date than the king; it was named thus by Heinrich Schliemann and the name has been used ever since.The historicity of the Trojan War, to which Schliemann sought to connect both Mycenae and Hisarlik, is a matter of long-standing and ongoing debate.

source: https://en.wikipedia.org/wiki/Treasury_of_Atreus