The largest ships tended to grow a belly or become wider in the middle, and the deck tended to curve inwards, making the tips of the masts move closer together. To avoid this, the Egyptians used a long, stiff reed running from bow to stern; the Romans used a large horizontal tree-trunk instead which they called the “supporting beam”.
A beam (or should we say a whole tree) was what the first ships to throw thousands of kilometres of telegraph cable overboard needed two thousand years later. Without such beam, they would never have been able to carry the massive weight required for laying the first transatlantic communications cable.