| 1 | Roman mile | = | 1000 passus | = | 4854 | English feet. |
| 1 | Old English mile | = | 1000 paces | = | 5090 | "" |
| 1 | Modern Statute " | = | = | 5280 | "" | |
| 75 | Roman miles | = | = | 1 degree. | ||
| (or 75.09 to be exact) | ||||||
| 4 | Roman miles = 19,416 ft., English = 1 marine league. | |||||
| The earth's circumference | = | 21,600 nautical miles, or | ||||
| = | 24,874 to 25,020 statute miles. | |||||
| A degree on the equator | = | 69.1 to 69.5 statute miles. | ||||
The Tordesillas geographers, in 1494, gave 21.625 leagues to the equatorial degree. They were wrong, but followed Eratosthenes, who made the globe 1-16th larger than it really is.
Vespucci, following Ptolemy and Alfragan, figured 6000 leagues, or 24,000 Roman miles, as the measure of the earth's circumference; so that dividing by 360, 16⅔ leagues made a degree.
Columbus, following various Arabian geographers, made the degree 56⅔ miles, or 14⅙ leagues.
All this confusion goes back to some deductions based on Ptolemy.
By 1517, according to Navarrete, the valuation of 17½ leagues to the degree had become general. At the treaty of Zaragoza, in 1529, that ratio was admitted on both sides.
The correct figure is very close to 17½ leagues.
All ancient calculations were based on dead reckoning. The log-line did come into use until 1521.
See Vivien de Saint-Martin, Le Nord de l'Afrique dans l'Antiquité grecque et romaine, Paris, 1863: p. 197.
Samuel Edward Dawson: The Line of Demarcation of Pope Alexander VI, and that of the Treaty of Tordesillas, in Transactions of the Royal Society of Canada, 1899, Vol. V. § 2, pp. 467 ff.
1. Berenice. (named for the mother of Ptolemy Philadelphus), is identified with Umm-el-Ketef Bay, below Ras Benas, 23° 55′ N., and about 35° 35′ E. It is 258 Roman miles, or 11 days, from Coptos, by a road across the desert. There are ruins still visible, even the arrangement of streets being clear; in the center is a small Egyptian temple with hieroglyphics and bas-reliefs of Greek wormanship. There is a fine natural harbor, but the bar is now impossible in low water; and Strabo (XVI, IV, 6) mentions dangerous rocks and violent winds from the sea.
At the time of the Periplus, Berenice seems to have been the leading port of Egypt for the Eastern trade, and was probably the home of the author.
