Before considering the individual sounds in detail, it is important to note that wherever a double consonant is written in Latin it stands for a correspondingly lengthened sound. This is clearly seen from its effect on the quantity of a preceding syllable, the first syllable of e.g. accidit or Me always being ‘heavy’ (see p. 89) although the vowel is short. Quite apart from metrical considerations, it is necessary to observe this in pronunciation, since otherwise no distinction will be made between such pairs as ager and agger, anus and annus. English speakers need to pay special attention to this point, since double consonants are so pronounced in English only where they belong to separate elements of a compound word—as in rat-tail, hoppole, bus-service, unnamed, etc.; otherwise the written double consonants of English (e.g. in bitter, happy, running) have the function only of indicating that the preceding vowel is short. The English compounds in fact provide a useful model for the correct pronunciation of the Latin double (or ‘long’) consonants.

In early systems of Latin spelling, double consonants were written single; the double writing does not appear in inscriptions until the beginning of the second century B.C. Ennius is said to have introduced the new spelling (cf. Festus, under solitaurilia), but in an inscription of 117 B.C. the old spelling is still more common than the new. The single spelling in such cases does not of course indicate single pronunciation, any more than the normal single writing of long vowels indicates a short pronunciation.