One may be skeptical of the overall contribution of Hellenistic science — its relative disconnection with practical application, or its failure to document the significant revolution represented by hydraulic energy. But the incontestable fact remains that in the study of the science and techniques of Antiquity preceding the Middle Ages, one cannot avoid marking pre — and post-Alexandria. The Hellenistic period represents a watershed, or divide, that is reflected in the two distinct parts of this book.
The earliest technology appeared before the turmoil that followed the epic reign of Alexander the Great. The elements of this technology can be briefly listed in the order of their appearance as follows:
— dams, made of rocks or earth, whose earliest traces are found on the Syro — Mesopotamian steppes at the end of the IVth millennium BC (Jawa, Khirbet el — Umbashi); the characteristics of the oldest of these dams are summarized in Table 10.1.
— derivation canals, sometimes created through cut-and-fill on the floodplain, with gates and guide vanes of stone; the oldest of the major works of this kind are probably those in the ancient land of Sumer, in the IVth millennium BC, but the genesis of this technology really belongs to all of the fertile crescent.
— drainage facilities, sewer systems of stone, bricks, or clay; we have seen them in the ancient cities of the Indus, in Sumerian settlements; they are particularly prominent in Crete.
— navigation canals, necessary adjuncts of the cities of lower Mesopotamia, for each Sumerian city has its own port; on the middle Euphrates, the Semiramis canal and the nahr Daourin are surely the oldest; in China, from the 5th century BC, the Hong canal connects the basins of the Yellow River to those of the Yangtze;
— the sailing vessel, first appearing in the Persian gulf, then in Egypt and the Aegean Sea;
— water supply systems, whose technology seems to first appear in Minoan Crete;
— and, somewhat of a special case since it is really an evolutionary technique that is conceived during the iron age: the qanats.
From the great cauldron of ideas that was Alexandria emerged the principles of hydrostatics, and the fundamental understanding of the effects of pressure. The inverse siphon and the pressure conduit are used in water supply systems. And hydraulic energy makes its appearance in the form of the watermill and the noria, two systems destined to see considerable development in the Middle Ages — the noria in the East and Far East, the water mill everywhere. The blossoming of hydraulic technology in the Middle Ages is seen in the mills dotting the landscape from the Atlantic to the Sea of Japan. Later, we can credit the Persians with the idea of the windmill, and the Chinese with the axial rudder and modern sail, as well as the navigation lock.
