Why were early oared warships built long and narrow?

Early oared warships were built long and narrow primarily to meet the essential requirements of naval warfare: speed, the ability to maneuver at any time in any direction, and the need to accommodate a substantial number of fighting men.1

In contrast to trading vessels, which were designed to be rounder to maximize tonnage and cargo capacity, the long, narrow hull of a warship allowed for a more efficient arrangement of oarsmen. This design provided the necessary speed and agility for tactics such as ramming, which became a standard feature of galley combat in the Mediterranean. While these low-sided, elongated vessels were effective for their specific military purposes, their design made them vulnerable to being swamped by swells in larger seas, a limitation that eventually influenced the evolution of ship design as naval needs and tactics changed over time.213