Old Latin is the
archaic form of
Latin before it had developed into the literary standard known as
Classical Latin. It is attested in numerous
inscriptions and quotations in later writers, and many features may be reconstructed from internal evidence.
Even Caesar, Cicero, and Virgil themselves used slightly different forms from those later codified and today studied as classical: for example caussa with double S, and optumus with a U. The spellings causa, optimus were fixed about the end of the Republican, or beginning of the Augustan period, the latter part of the last century BCE. The playwrights Plautus and Terence, though usually treated as classical authors, were considerably earlier, and show archaic features.
Latin was a member of the Italic branch of the Indo-European family. In ancient times languages closely related to Latin still existed in neighbouring parts of Italy: they include Oscan, Umbrian, and Sabine. None survived beyond antiquity. These were close enough to influence each other. Latin was probably also influenced by the unrelated Etruscan, whose alphabet was adapted to create the Roman one.
Romans of the classical period were already so distanced from the language of the earliest inscriptions that they found many of them unreadable.
Consonants
The sound H began to disappear early, and had gone in
Vulgar Latin. In Classical Latin it was probably a learned sound, with people having to memorize which words to use it in, and correcting each other. Some words with H loss became standard, such as
hanser 'goose' (both from
PIE *
ghans-) and
harena 'sand' (
Sabine fasena). These became
anser and
arena even in correct style. Conversely, an
unetymological H was added to several words:
umor and
umidus became
humor, humidus. Medially, loss of H gave rise to forms such as
nemo 'nobody' from
ne-homo 'no person'.
A single S between vowels changed to R. This (partly) explains pairings such as robur 'strength', robustus, and alternations between nominative and stem such as os 'mouth' ~ oris (from *osis), and corpus 'body' ~ corporis. A double S, as in caussa, later changed to single S, but was no longer affected by the earlier change to R.
The Roman alphabet derived from the Etruscan, and at first used some peculiar writings because of that. In early inscriptions all three letters C K Q were used, depending on the following vowel, ci ce ka qo qu, but this was later regularized to C, with Q reserved for the KW-sound as in English. C was also used for G, which did not exist in Etruscan, until the 3rd century BCE when the distinguishing stroke was added, traditionally by a slave called Spurius Carvilius Ruga. The new letter G was placed in the alphabet where Greek had zeta, a sound not needed in Latin.
Etruscan had no F. The shape 'F' was the old Greek letter digamma, pronounced W. Latin at first wrote their F-sound as FH, i.e. WH, but later wrote this as F and began to use their vowel V (i.e. U) with a consonant value of W. Thus, an early inscription on a fibula reads MANIOS MED FHEFHAKED NVMASIOI - classically, Manius me fecit Numasio 'Manius made me for Numasius'. (This, traditionally regarded as the earliest Latin inscription, is now believed by most experts to be a forgery: it isn't entirely settled. But even if it's fake it illustrates the old usage of FH.)
Other consonant changes that happened well before the Old Latin period are worth mentioning here because of the light they throw on grammatical alternations. TS and DS became S, and GS became KS (written X). Instead of worrying why frons 'front' changes to frontis in the genitive, while frons 'leaf, frond' changes to frondis, a lot of memory is saved by regarding front- and frond- as the basic forms, and applying the consonant simplification rule after the nominative ending -s. Likewise reg- regularly changes to rex, ped- to pes, and aetat- 'age' to aetas. Final KTS simplifies to KS, and SS to S: noct- ~ nox 'night', and oss- ~ os 'bone'. In words like corpos- ~ corpus you also get the medial change S > R (in genitive corporis) and a final vowel change (see below).
The same changes occur in the perfect, in those verbs that have a basic ending -si: augeo ~ auxi 'grow', rideo ~ risi 'laugh', ardeo ~ arsi 'burn' are quite regular.
Vowels
In old inscriptions we see words such as
oinos for later
unus,
oino or
oinom for
unum, and
optumos for
optimus. So OI changed to long U, except that finally it became long I, as in the masculine nominative plural
-i (cf. Greek -οι).
Final -OS and -OM raised to -US and -UM. The final M had already been lost, causing the preceding vowel to become nasalized (see Classical Latin pronunciation for details). This vowel was written in Old Latin as -O or -OM.
There are numerous words where U changed to I next to a labial consonant, as in optumus 'best', lacruma 'tear', pontufex. There was probably an intermediate pronunciation with Ü. The spelling was officially changed by Julius Caesar.
The accent in the ancestral Proto-Indo-European was a variable pitch accent. In Old Latin it had changed to a strong initial stress accent. This might have been under Etruscan influence, because that language was also initially stressed and caused significant reduction of following syllables. In Classical Latin it had shifted to a basically penultimate stress accent. This initial stress caused changes to subsequent unstressed vowels, and these changes were kept even when the stress later shifted onto them. The main change is of a short vowel to I before one consonant and E before two.
So teneo 'hold' gives retineo 'retain', past participle retentum. The stem cap- appears with A in capio and captivus, and E and I in the words giving rise to our inception, incipient. This is why there is no word 'ept' that 'inept' is the negative of: it comes from 'apt'.
The letter L was apparently a dark L at the end of a syllable, as in English, and had an effect on the preceding vowel: so Greek Sikelos 'native of Sicily' became Sicolos then Siculos. W (written V) also had a lowering effect on O: the words volgus, servos, equos were not changed to the more familiar vulgus, servus, equus until the Augustan period.
There are many more individual changes I could catalogue, but this has gone on long enough. A warning: not all alternations can be explained by these rules. Other forces were at work, such as analogy.