sixteen letters

“He conceives the Ouigour alphabet of sixteen letters to have been formed from the Syriac, and introduced by the Nestorian Christians. —”

The History of the Decline and Fall of the Roman Empire

“(Nordische Geschichte, p. 481, &c.,) who considers their sixteen letters to be a corruption of the Roman alphabet, post-Christian in their date, and Schlozer would attribute their introduction into the north to the Alemanni.”

The History of the Decline and Fall of the Roman Empire