Canals are usually ranged under one or other of three great categories, namely:— 1. For purposes of navigation. 2. For irrigation, and 3. For domestic water supply. Under the first heading there are many different descriptions of waterways, the more important being— _a._ Canals intended for the purpose of connecting oceans or seas, such as those of Suez, Panama, the North Sea, and Nicaragua. _b._ Canals for the purpose of bringing the sea to an inland town, such as those of Manchester and St. Petersburg. _c._ Canals designed to connect and complete communication between different rivers or lakes, like the Grand Canal of China, the Erie Canal, and the Welland Canal. _d._ Canals constructed for the purpose of enabling the obstructions caused by falls or cataracts on natural waterways to be overcome by artificial means. As water transport by the most efficient and most economical means practicable is the _raison d’être_ of the present work, we shall speak for the most part of navigation canals only. The chapters that follow will show, that canal navigation has not only an interesting, but a very ancient history. It is, indeed, so long since canals were first projected and constructed that it is extremely difficult to trace their beginnings. The Bœotian Canal, which is said to have drained the Lake Mœris by several channels carried in tunnels through high mountainous barriers, is of such fabulous age as to have led fiction to usurp the place of history, and even of tradition, when describing the work at a period of time so far back as prior to the conquest of Greece by Rome. The celebrated canals of China have been assigned an unknown antiquity, but trustworthy representations have led authorities to conclude that they are scarcely older than the works in the Deccan. At all events, they date from less than 900 years ago, a century subsequent to the first irrigation of Valentia. In Spain, the Moors constructed canals to connect inland places with rivers, particularly the Guadalquiver, and connecting Granada with Cadiz. They also introduced, when they conquered that country, their own system of irrigation, with the customs and laws relating thereto, which are followed at the present hour without material change.