At the top of the big rock that rises above Vlacherna there was a medieval castle, the castle of Bezenikos. 
From this castle, in 1458, the Greeks mounted a heroic resistance against the troops of Mohammed II the Conqueror. The same thing happened in 1826 during the advance of Ibrahim's hordes, during the revolution of 1821.
Source: UNIVERSITY OF PATRAS 
arcadia.ceid.upatras.gr