The inscription is spread over six lines: NON // DICE // REIL // LESE // CRITA // ABBOCEThis may be divided into words as non dicere ille secrita a bboce ('don't say the secrets aloud'), referring to Christian mysteria or secret prayers to be recited under one's breath.
[2] The inscription has to post-date the fresco on which it is written, which can itself be dated to the 6th or 7th century on stylistic grounds (thus establishing the terminus post quem).
The terminus ante quem can be estimated on the following grounds: Altogether these point to a date around the beginning of the 9th century.
At first the word had been written boce, but afterwards, either the same writer or another felt that the spelling did not reflect his pronunciation closely enough, and so he inserted an additional ⟨b⟩ in superscript.
This hints at the pronunciation of the Roman dialect at the time, characterized on the one hand by syntactic doubling (still typical in the area today) and on the other hand by betacism or the merger of Latin /b/ and /w/ (thus Latin ad vōcem resulted in a bboce).