Melissus was a pre-Socratic philosopher from the ancient Greek city of Samos, active in the 5th century BCE. He is best known for his contributions to the philosophy of Eleaticism, which emphasizes the idea of a singular, unchanging reality. Melissus argued against the existence of plurality and change, asserting that what truly exists is eternal and indivisible. His work is primarily preserved in fragments, where he presents his arguments for the nature of being. Melissus contended that if something exists, it must be infinite and unchanging, challenging the views of other philosophers like Heraclitus, who believed in constant change.