Isopsephy (; isos meaning "equal" and psephos meaning "pebble") or isopsephism is the practice of adding up the number values of the letters in a word to form a single number. The total number is then used as a metaphorical bridge to other words evaluating the equal number, which satisfies isos or "equal" in the term. The early Greeks used pebbles arranged in patterns to learn arithmetic and geometry, which corresponds to psephos or "pebble" and "counting" in the term. Isopsephy is related to gematria: the same practice using the Hebrew alphabet. It is also related to the ancient number systems of many other peoples (for the Arabic alphabet version, see Abjad numerals). A gematria of Latin script languages was also popular in Europe from the Middle Ages to the Renaissance, and its legacy remains in code-breaking, numerology, and Masonic symbolism today (see arithmancy). History Until Arabic numerals were adopted and adapted from Indian numerals in the 8th and 9th centuries AD, and promoted in Europe by Fibonacci of Pisa with his 1202 book Liber Abaci, numerals were predominantly alphabetical. For instance in Ancient Greece, Greek numerals used the alphabet. It is just a short step from using letters of the alphabet in everyday arithmetic and mathematics to seeing numbers in words, and to writing with an awareness of the numerical dimension of words. An early reference to isopsephy, albeit of more-than-usual sophistication (employing multiplication rather than addition), is from the mathematician Apollonius of Perga, writing in the 3rd century BC. He asks: "Given the verse: (), what does the product of all its elements equal?" More conventional are the instances of isopsephy found in graffiti at Pompeii, dating from around 79 AD. One reads "" Another says, " " Suetonius, writing in 121 AD, reports a political slogan that someone wrote on a wall in Rome: which appears to be another example. In Greek, Νερων, Nero, has the numerical value 50+5+100+800+50=1005, the same value as (idian metera apekteine) — "He killed his own mother", (10+4+10+1+50) + (40+8+300+5+100+1) + (1+80+5+20+300+5+10+50+5). A famous example is 666 in the Biblical Book of Revelation (13:18): "Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six." The word rendered "count", , psephisato, has the same "pebble" root as the word isopsephy. The Greek