Caementum canalem obstruit.

You can tell mainly from the endings.

• caementum is nominative singular, so it is the subject
• canalem is accusative singular, so it is the direct object

So the sentence means that caementum is doing the action, and canalem is receiving it.

Even though English relies heavily on word order, Latin relies much more on case endings.

Because it is the accusative singular form of canalis.

This noun belongs to the third declension, and many third-declension nouns form the accusative singular with -em.

So:

• nominative: canalis
• accusative: canalem

Here, the verb obstruit takes a direct object, so canalis has to appear in the accusative: canalem.

Good question: -um can be misleading, because it is often accusative in some nouns, but here caementum is nominative singular.

That happens because caementum is a neuter second-declension noun. In neuter second-declension nouns:

• nominative singular = -um
• accusative singular = also -um

So the form caementum could be nominative or accusative by itself. In this sentence, it is nominative because canalem is clearly marked as the accusative object.

Obstruit is a verb meaning blocks, stops up, or obstructs.

Grammatically, it is:

• present tense
• active voice
• indicative mood
• third person singular

It comes from the verb obstruere, meaning to block or to obstruct.

So obstruit means he/she/it blocks.
Since the subject is caementum, the natural English translation uses it blocks.

Because Latin usually does not have articles like English the or a/an.

So caementum canalem obstruit could be translated, depending on context, as:

• The cement blocks the channel
• Cement blocks the channel
• The rubble blocks a canal

Latin often leaves that distinction to the context.

It matters much less than in English.

Because the endings already show the grammatical roles, Latin can often change the order without changing the basic meaning. For example, these would still mean essentially the same thing:

• Caementum canalem obstruit
• Canalem caementum obstruit
• Obstruit caementum canalem

However, changing the order can change the emphasis. The original order is straightforward and neutral: subject – object – verb.

Because Latin verbs usually already include the subject information in their ending.

The ending -t in obstruit tells you the verb is third person singular: he/she/it blocks.

So Latin does not need to add a separate pronoun unless it wants extra emphasis.

Yes. English obstruct comes from the same Latin root.

That can be very helpful when learning vocabulary:

• Latin obstruere = to block up
• English obstruct = to block

So obstruit is a nice example of a Latin word that looks familiar to an English speaker.

You would normally learn them like this:

• caementum, caementi = cement, rubble, stone chippings
• canalis, canalis = channel, canal, pipe
• obstruo, obstruere, obstruxi, obstructum = to block, obstruct

Latin dictionaries usually list nouns with the nominative singular and genitive singular, and verbs with their main principal parts.

A classroom pronunciation might be roughly:

kai-MEN-tum ka-NAH-lem ob-STROO-it

More traditionally reconstructed Classical pronunciation would make:

• c always hard, like k
• ae like the ai in aisle
• u like oo
• i like ee when pronounced as a vowel

So:

• caementum ≈ kai-MEN-tum
• canalem ≈ ka-NAH-lem
• obstruit ≈ ob-STROO-it

Sometimes in later or learner-oriented contexts it may be glossed that way, but historically caementum in Classical Latin often refers more to rough stone, quarry stone, or rubble rather than modern manufactured cement.

So depending on the course or context, the English meaning shown to the learner may be simplified. Grammatically, though, that does not affect how the sentence works.