Tumulus Arapomagoula is a grave of Aristodamos, the tyrant of Megalopolis1.
See:
Pausanias Description of Greece with an English Translation by W.H.S. Jones, Litt.D., and H.A. Ormerod, M.A., in 4 Volumes. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1918
Stamatis Fritzilas: Grave Stelai and Burials in Megalopolis, in Η. Cavanagh, W. Cavanagh, J. Roy (ed.), Hοnouring the Dead in the Peloponnese. Proceedings of the conference held at Sparta 23-25 April 2009, CSPS Online Publication 2, The University of Nottingham, pp. 102, 114 ff