The great civilizations that appeared and disappeared in the Middle East for centuries before the Roman period were dependent on water. Babylon, for example, flourished about 6,000 B.C.E. The city was famous for its gardens and fed a huge population in an area of limited rainfall. Water was brought in from distant mountains by means of aqueducts, canals, and underground tunnels.
Planning and building these water systems required great skill, and the men (plumbers) who built them had to rely on just three or four primitive tools—the level, the T-square, the plumb line, and a knotted cord. The level was usually a dish-like container filled with water or oil. The T-square was wooden and came in many sizes. The plumb on the long plumb line was a small but heavy pointed object, usually lead.
Not only did those early plumbers build great and enduring water systems, but they also built palaces and temples. The plumb line was essential to keep the square square and to keep the level level. Without that length of cord with its lead weight, the great pyramids of Egypt would never have been so perfectly aligned, and the lovely cathedrals of medieval Europe would have fallen down long ago.
Today we still use the words level, square, and plumb, especially in the building trades. The tools have hardly changed during the last few thousand years.