....in speech, Romans often dropped the final syllable (especially a sibilant). And the bolded vowel letters (sounds), are my attempt at marking a meter of some sort.

how do we know that when Romans talked they did this? I can understand if we knew from their writings, but how do we know they did it while talking?

Did you know there are some really old Latin texts, some about grammar, etc? We don't actually know exactly how they spoke, but there are several languages around that (are presumed to) have retained the flavour of spoken, or idiomatic Latin. Italian is one--it's believed to be phonetically the closest to how Latin was actually spoken.

The elision of a final syllable was, and is, a well known linguistic feature, not just in Latin. A final "s" was always optional, in Vulgate Latin, say. It's easier to drop a few syllables, and rhythm is more important than grammar, also it makes some meanings ambiguous--it's easier to do this in a language like Latin. Latin and Greek have had a lot of influence on spoken languages, esp. in Europe.

I'm curious about the elision of final syllables in Latin too. It's such a powerful force in the evolution of many languages, that you'd expect it to be carried forward in Latin's descendants. But it's not. The final syllables are well-preserved in Italian, Spanish, Portuguese and Romanian. The only one in which elision is widespread is French, which is unique because of the strong influence of the Franks' native Germanic tongue with its much more compact phonetics. (French has lots of telltale signs of Germanic influence, like its gargled R, use of the present perfect instead of preterit tense--tu as aimé instead of tu aimas--and all those wacky umlauted vowels.)

Catalan has some elision, but it's so closely related to Spanish and Portuguese that it just has to be a recent phenomenon. I don't know about Occitan (what we used to call Provençal).

As to the question about how we know anything about the pronunciation of ancient languages, that's some serious detective work. There are two primary ways. One is the observations of foreigners, borrowing words and transcribing the sounds in their own language, or just writing about them as linguists like we do. The other is poetry, because rhyme and meter serve as ways of comparing words.

The speech elision mechanism is probably responsible for the loss of all those inflections on Latin nouns and verbs.
Nowadays we use the same word for the thing as for the action, and we use participles as nouns ("seeing", "reading"), English is disordered, compared to orderly old Latin with its fairly consistent conjugations (only 4, and some irregular verbs), and declensions (5, but there are sub-groups). Once words started losing bits off the end, they began to converge to the same, root form (like the Latin imperative, say).

Latin isn't that ancient, and it was spoken continuously by a lot of people, mostly clergy, but it was the language of Science, along with Greek, during the Renaissance. Back then, if you didn't speak and read Latin, you didn't know much.

...Latin isn't that ancient, and it was spoken continuously by a lot of people, mostly clergy, but it was the language of Science, along with Greek, during the Renaissance. Back then, if you didn't speak and read Latin, you didn't know much.

the majority of the people didn't speak it, let alone read it. Its why the church held onto it.
Its also why its become a dead language

The speech elision mechanism is probably responsible for the loss of all those inflections on Latin nouns and verbs.I think it was more likely because as the empire broke down the common folk came to dominate the development of the language. Common folk don't speak in complicated sentences so they don't need five cases for their nouns to prevent misunderstandings. In any case, most of the noun inflections didn't add a syllable, just changed the final consonant, so there's not much economy at work. Verb inflections do add syllables, and Spanish, Italian, Portuguese and Romanian nonetheless retained a good portion of the verb inflection paradigms. Not only that, but they added extra syllables by making pronouns mandatory even when the inflection on a verb indicates the person. In Latin you could just say amo, but you have to say yo amo, eu amo, io amo in Spanish, Portuguese and Italian, respectively. In Romanian they even changed it to the cumbersome ending -esc and still require the pronoun. "I love" is eu iubesc. You can only omit the pronoun in poetry. Americans love to omit them in colloquial speech and that instantly brands us as foreigners if our accent doesn't.
Nowadays we use the same word for the thing as for the action, and we use participles as nouns ("seeing", "reading").That's just a collapse of two proto-Germanic inflections. In German the present participle (used as a verb) ends in end, but a gerund (used as a noun) ends in ung. English has merged the two into "-ing".
English is disordered, compared to orderly old LatinI'd call that a bad choice of words. :) The upshot of all this is that in English, word order is very rigid, whereas in Latin, with its inflections keeping the syntax straight, it was possible to move words all around the sentence without confusing anybody. Chinese has no inflections at all, and its word order is even more stringent than ours. Japanese inflections make Latin look simple: verbs are conjugated by the gender of the speaker and by the social relationship between the speaker and the person addressed, but word order is still fairly rigid.
Once words started losing bits off the end, they began to converge to the same, root form (like the Latin imperative, say).I'm only well versed in Spanish grammar, but I'm pretty sure the imperatives have hardly been simplified at all from Latin. Second person singular imperative is third person singular indicative. Second person plural imperative has its own unique inflection. I think that's the same as Latin. Since Spanish has co-opted third person pronouns as polite forms of "you," it had to come up with third person imperatives, but it uses the subjunctive. I think that's also the same as Latin.
Latin isn't that ancient, and it was spoken continuously by a lot of people, mostly clergy. . . .Make that "only" the clergy :)
. . . .but it was the language of Science, along with Greek, during the Renaissance. Back then, if you didn't speak and read Latin, you didn't know much.That's because throughout the Dark Ages, the only people who kept literacy alive in Europe were monks, who just happened to be the only people who knew Latin! So immediately after the Enlightenment, everything anybody wanted to read was in Latin, or the really ancient stuff was in Greek (or Aramaic). As soon as the printing press was invented, there was enough reading material available to motivate people other than scholars to learn to read and write. Those people didn't know a word of Latin so contemporary popular writing was done in the modern national languages. Administrative writing soon followed, and scholars eventually joined the trend. The printing press encouraged them to translate the ancient texts from Latin and Greek into the language of the common folk so knowing Latin and Greek became less important.
the majority of the people didn't speak it, let alone read it. Its why the church held onto it.I'm not sure that's a fair statement. There was a lot of inertia at work in the era before printing, when there were not very many copies of a text. If there were only a few hundred hand-written copies of the Aeneid you're better off to leave them in Latin because the only people who can read them probably can read Latin.
Its also why its become a dead languageA case can be made for calling Latin "Old Italian." There's a famous story of a 20th century schoolboy who was assigned to write a poem in Latin. He turned one in in Modern Italian and the teacher started lambasting him. He stopped him and said, "Please look again." Turns out it was identical in Italian and Latin. Sorry I don't have the text handy but I've seen it and it's a true story.

...as the empire broke down the common folk came to dominate the development of the language. Common folk don't speak in complicated sentences so they don't need five cases for their nouns to prevent misunderstandings. In any case, most of the noun inflections didn't add a syllable, just changed the final consonant, so there's not much economy at work."Complicated sentences", I assume to mean "correctly spoken"?
Latin inflection (nouns, verbs, adjectives) at the end of a word, most definitely adds syllables, particularly with plural forms. Would you like to see some examples that demonstrate this?
Common parlance usually means the appearance of "easily spoken" (simpler) forms, so words tended to find a lowest state of "pronunciative effort"--which still conveys meaning.
English is (very) contextual, Latin isn't.

The rhythm (meter) is important in Latin, word order is modified by the meter requirements; iambus, dactyl, spondee, etc, convey meaning too. The morphemes are already sememes in Latin.

In a context-free language (like some programming languages), meaning or functionality is conveyed with the word (morpheme, or message from a grammar: an alphabet of symbols with production rules).
As each symbol arrives, it's passed through what linguists call a semantic(s) net, so in a context-ful language like English, you have to wait for context to appear, in a phrase or sentence. The semantic network has to stack symbols until other meaning has been processed, then the symbols (morphemes) "catch up" with the input.

Latin word-order, since each word arrives with its meaning (it's inflected), is used to convey different kinds of rhythm instead, so this is added, but intentional meaning. Poetry, in any language, uses rhythm, too. English vs Latin poetry illustrates how the two languages employ meter differently, or what sort of room to move they each have.

Of course, Latin, as any language, isn't context-free, and English doesn't depend on context necessarily. But English tends to rely on phrasing (the meaning is spread over a group of morphemes), and Latin doesn't; word order has a different general kind of function in both.

Algonquin and other native or aboriginal languages have interesting grammars, with meaning implied (sememes between or beneath the morphemes delivered by a speaker).

how do we know that when Romans talked they did this? I can understand if we knew from their writings, but how do we know they did it while talking?I thought they had unearthed an ancient 8-track tape with some argument on it... about someone not being wanted in power or something - and then definite sounds of multiple stabbings.

I might be wrong, though. :D