(Μέγιστος; Mégistos). Aside from the Rhyndacus and the Tarsius, the largest river in northern Mysia (cf. Str. 12,8,11; Plin. HN 5,142; Pol. 5,77,8), modern Simav Çayı that like the Tarsius flows into the Rhyndacus north of Miletupolis. Attalus  I was encamped on the M., north of the Pelecas Mountains with the Galatian Aegosages on his campaign against Achaeus , when he experienced a lunar eclipse on 1 January 218 BC. A relief of Apollo Mekastenos is probably also reminiscent of this river .
Schwertheim, Elmar (Münster),
“Macestus, Mecestus”, in:
Brill’s New Pauly, Antiquity volumes edited by: Hubert Cancik and , Helmuth Schneider, English Edition by: Christine F. Salazar, Classical Tradition volumes edited by: Manfred Landfester, English Edition by: Francis G. Gentry.
Consulted online on 17 January 2019 <http://dx.doi.org/10.1163/1574-9347_bnp_e719140>