Our pound, settled at its present Imperial standard in the time of Queen Elizabeth, was then found to have risen slightly since the time of Edward III. It was found to have increased by about 8 grains. The ounce, now = 437-1/2 grains, had been 437 grains, the same weight as the ounce of Egypto-Roman pound, the Roman libra.[22] There is every reason to believe that this Roman standard passed to Britain, and that the libra, raised to 16 ounces, became the commercial pound, afterwards known as Averdepois, and now the Imperial pound.
The modern _libbra_ is 12 ounces = 436·27 grains in Rome, 436·66 in Florence.
When the Romans took the Alexandrian talent as the standard of their new libra-system, they divided it into 125 libræ, which were 1500 ounces or double-shekels, each ounce = 437 grains.
When the Arab Caliphs conquered the southern and eastern Mediterranean countries, they found in Egypt the Egypto-Roman pound, 1/125 of the Alexandrian talent; they adopted it, and divided it for coin-weight purposes into 72 mithkals, just as the Roman Emperors had divided the old As pound into 72 aurei; so 6 mithkals = the libra-ounce of 437 grains, just as 6 aurei = the As-ounce of 420-2/3 grains. It is not improbable that the survival of the Roman commercial pound in Saxon England was strengthened by commercial and scientific relations with the Moors of Spain. King Offa of Mercia struck a gold coin with an Arabic inscription, dated 157 of the Hejira = A.D. 774.
However this may have been, there seems no doubt that the Roman pound, raised to 16 ounces, was the standard of England before as after the Norman conquest, and there is no evidence of it having ever been in abeyance. In early Plantagenet times there was a sexdecimal series of weights:
There was also the Hundredweight, of which 20 made a ton of 2000 lb.; and 20 weys made a Last of approximately 5120 lb. or 2-1/2 tons.
The pound was divided into 16 ounces, each = 437 grains, and the ounce into 16 drams or drops = 27·3 grains.
Both before and after the Conquest there was another pound used in the mints, like the As in Rome. It was of Tower, or Cologne-marc, standard. There were doubtless many local variations of commercial standard, especially in measures of capacity, and it was the necessity of checking these which made King John and his successors declare that ‘there should be one standard throughout our kingdom, whether in weights or in measures.’