As civilization developed, so too did the need for units of measurement. These were required for numerous tasks such as: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials.
Sources of Information
Weights and measures have taken a great variety of forms over the course of history, from simple informal expectations in barter transactions to elaborate state and supranational systems that integrate measures of many different kinds. Weights and measures from the oldest societies can often be inferred at least in part from archaeological specimens, often preserved in museums. The comparison of the dimensions of buildings with the descriptions of contemporary writers is another source of information. An interesting example of this is the comparison of the dimensions of the Greek Parthenon with the description given by Plutarch from which a fairly accurate idea of the size of the Attic foot is obtained. Because of the comparative volume of artifacts and documentation, we know much more about the state-sanctioned measures of large, advanced societies than we do about those of smaller socieities or about the informal measures that often coexisted with official ones throughout history. In some cases, we have only plausible theories and we must sometimes select the interpretation to be given to the evidence.
By studying the evidence given by all available sources, and by correlating the relevant facts, we obtain some idea of the origin and development of the units. We find that they have changed more or less gradually with the passing of time in a complex manner because of a great variety of modifying influences. It is possible to group official measurement systems for large societies into historical systems that are relatively stable over time, including: the Babylonian system, the Egyptian system, the Phileterian system of the Ptolemaic age, the Olympic system of Greece, the Roman system, the British system, and the metric system.
Earliest known systems
The earliest known uniform systems of weights and measures seem all to have been created at some time in the 4th and 3rd millennia BC among the ancient peoples of Egypt, Mesopotamia and the Indus Valley, and perhaps also Elam (in Iran) as well.
The system attributed to the Indus Valley Civilization (ca. 2600 BC) is sometimes cited as particularly accurate. Based on an ivory scale found in Lothal, their smallest unit corresponded to approximately 1.704 mm (0.067 in), the smallest division ever recorded on a scale of the Bronze Age.
Early Babylonian and Egyptian records and the Hebrew Bible indicate that length was first measured with the forearm, hand, or finger and that time was measured by the periods of the sun, moon, and other heavenly bodies. When it was necessary to compare the capacities of containers such as gourds or clay or metal vessels, they were filled with plant seeds which were then counted to measure the volumes. When means for weighing were invented, seeds and stones served as standards. For instance, the carat, still used as a unit for gems, was derived from the carob seed.
Units of length
The Egyptian cubit, the Indus Valley units of length referred to above and the Mesopotamian cubit were used in the 3rd millennium BC and are the earliest known units used by ancient peoples to measure length. The units of length used in ancient India included the dhanus (bow), the krosa (cry, or cow-call) and the yojana (stage).