The later rams varied considerably in shape. The triple ram was sometimes made with the teeth pointing slightly downward, while others had an upward tilt. The lowest ram often extended farther forward than those above, the idea being that it would inflict severe injury about or below the water line, and that the upper rams, besides causing damage, would push the stricken vessel off the lower ram and let her sink without the assailant being dragged down by the head with her. The build of the ships rendered it necessary that an engagement should be fought on a calm sea, and daylight was preferred in order that the combatants could see what they were doing. As the fleets approached one another the commanders of the different vessels decided upon their individual opponents. Much skilful manœuvring ensued to ram the enemy or avoid a blow. The slaves strained at the oars while their taskmasters ran between the files of rowers and, with unmerciful blows from heavy sticks and whips, stimulated them to still greater exertions if possible. Poor slaves, mostly prisoners of war, their prospects were gloomy in the extreme! If their ship were rammed some of them were sure to be injured, and if she sank they went down with her, fastened to their places and having no chance of escape. If the oars were disabled in the collision between the ships the rowers were bound to receive violent blows from the inboard end of the oars, or to be cruelly pierced by splinters of wreckage. Showers of missiles from the opposing ship fell upon the helpless wretches. In later years, when the terrible Greek fire was added to the means of attack and defence, it contributed the prospect of being burnt alive to the other horrors of their situation. Victory meant no rejoicings for them. The wounded were of little account and could be dispensed with when slaves were to be had for the capturing, and it was easy to put them overboard to die the more quickly. Those who survived the battle unhurt or not too severely injured to recover rapidly, were retained. If their ship were vanquished they might look forward to greater cruelties as a punishment for their share of the defeat. If they belonged to the victors, they had only more battles, the torturing whips of their drivers, and insufficient food as their portion in life. Death came as a welcome relief to the slaves of victor and vanquished; in it lay their only hope of peace. When the Roman navy was at its best the ships were painted a colour which matched the waves, and the hulls were made as watertight as possible with tar. Occasionally in the later Roman ships layers of tarred cloth were placed outside the outer planking, and the hull was then lead-sheathed. Bronze nails and wooden pegs were used in fastening the timbers together, and some ships were so built that they could be taken to pieces and transported overland if necessary. Ships of three, four and five banks were even conveyed from the Mediterranean to the Euphrates.