The Ermioni Complex in the east of the Argolis Peninsula (Adheres), Peloponnesus, comprises a tectonically thickened (10-15 km) wedge of terrigenous, early Tertiary (Paleocene-Eocene) flysch, interleaved with thin, tectonically disrupted sheets of basic lava, massive sulfides, and metalliferous and pelagic sediments. Immobile trace-element analysis of the basalts in the Ermioni Complex suggests an oceanic, mid-ocean ridge, and/or subduction-related origin. The planktonic foraminifer Globotruncanita elevata in pelagic limestones depositionally overlying the basalts is Campanian-Maastrichtian in age. We propose that the basaltic slices represent fragments of a Neo-Tethyan ocean of Late Cretaceous age in the southern Greece area. The basin subsequently closed in the early Tertiary (Paleocene-Eocene), with trench-type Flysch accumulation and accretion of oceanic lava slices. The new evidence contradicts the current view that the Neo-Tethys was fully sutured by Early Cretaceous time in this area.