The practice of reading words as numbers: each letter carries a value, the word carries a sum, and matching sums are read as hidden kinship.
Documented
The king who measured his name
The first documented use is an 8th century BCE inscription of Sargon II of Assyria: the king states he built the wall of Khorsabad 16,283 cubits long to correspond with the numerical value of his name. How the sum was computed is still not understood. The Greek version, isopsephy, grew out of the Milesian habit of using letters as numerals, common by Alexander's era, and Hebrew letters appear as numbers in the record from 78 BCE. The system later became a pillar of Kabbalah.
Assessment: Documented from the Assyrian inscription onward, with the Greek-to-Hebrew transmission traced in the scholarly record. The practice is old; the oldest math is still unsolved.
Stories
I love her whose number is 545
The most human story in the file: a graffito from Pompeii, scratched before 79 CE, reads roughly, I love her whose number is 545. A lover hid a name in a sum, in a city full of people who could decode it. And the Sibylline Oracles turned it into scripture: the name Iesous, Jesus, sums to 888 in Greek, eight hundreds, eight tens, eight ones, a number early Christians read as triple perfection against the beast's 666.
Assessment: The Pompeii graffito and the 888 calculation are both documented. The lover's name is lost, which is somehow the perfect ending: the oldest gematria story is a secret that stayed secret.
Interesting claims
The alphabet was designed for this
The claim: alphabetic writing and number systems were never separate, letters were always quantities, so any text is a lattice of numbers and any sum you compute was always there, waiting. Stronger versions hold that temple dimensions, from the Parthenon onward, were set isopsephically, buildings as frozen calculations.
Assessment: The letters-as-numbers part is documented fact in Greek and Hebrew practice, no conspiracy required. The designed-temple layer is argued from pattern, not blueprint, and pattern is cheap when you choose the ruler. Filed as an intriguing frame with unprovable architecture.
Sources and further reading
Sargon II inscription, Khorsabad, 8th century BCE, the 16,283 cubit wall
Stephen J. Lieberman, Hebrew Union College Annual 58 (1987), Mesopotamian background
Pompeii graffito, I love her whose number is 545
Sibylline Oracles 1:395-400, the 888 calculation
Worth asking
If two unrelated words share a number, is that a message, a coincidence, or the arithmetic of any alphabet with enough words?