Dies sollemnis est, et longa pompa per forum procedit.

Because dies is in the nominative singular, which is the case normally used for the subject of a sentence.

In Dies sollemnis est, the basic structure is:

• dies = the subject, day
• est = is
• sollemnis = describes dies

So the sentence means The day is festive/ceremonial.

Sollemnis has to agree with dies in case, number, and gender.

Here, dies is:

• nominative
• singular
• masculine (in this sentence)

So the adjective must match it. The form sollemnis is the nominative singular form that works here.

This is a very common Latin pattern:

• puella bona = the good girl
• vir bonus = the good man
• dies sollemnis = the festive day

Even though sollemnis belongs to the third declension as an adjective, it still agrees with the noun it describes.

Usually dies is masculine, especially in ordinary use, and that is how it is being used here.

Latin learners often notice that dies is a bit special because it can sometimes be feminine, especially when it means a particular appointed day or date. But in most beginner contexts, you should think of dies as masculine unless you have a reason to do otherwise.

So here:

• dies = masculine
• sollemnis agrees with it

Yes, Latin sometimes omits forms of to be, especially in certain styles, but here est is perfectly normal and straightforward.

So:

• Dies sollemnis est = The day is festive

With est, the sentence is clear and complete. For a learner, this is the most expected form.

Et simply means and.

It joins the two clauses:

• Dies sollemnis est
• longa pompa per forum procedit

So the whole sentence is:

• The day is festive, and a long procession moves through the forum.

It is just the ordinary coordinating conjunction, like English and.

Because pompa is in the nominative singular, and it is the thing doing the action of procedit.

In the second clause:

• longa pompa = a long procession
• procedit = proceeds / moves forward
• per forum = through the forum

So pompa is the subject because the procession is what is proceeding.

Longa agrees with pompa.

Here pompa is:

• nominative
• singular
• feminine

So the adjective must match:

• longa = nominative singular feminine

That is why it is longa pompa, not longus pompa or longum pompa.

Because the preposition per takes the accusative case.

So:

• forum here is accusative singular
• after per, that is exactly what we expect

Per usually means through or along, and it regularly governs the accusative.

Examples:

• per viam = through the road / along the road
• per urbem = through the city
• per forum = through the forum

So foro would be wrong after per.

This is a very useful distinction.

• per forum = through the forum, emphasizing movement through the space
• in foro = in the forum, emphasizing location

So in this sentence, the procession is not just located in the forum; it is moving through it. That is why per is the natural choice.

Procedit is from procedere, which literally means to go forward, advance, proceed, or move onward.

Here it fits a procession very naturally:

• longa pompa per forum procedit = a long procession proceeds through the forum

Grammatically, procedit is:

• present tense
• third person singular
• active voice

It is third person singular because its subject, pompa, is singular.

Because it is a third person singular present form of a third-conjugation verb: procedere.

Very roughly:

• procedo = I proceed
• procedis = you proceed
• procedit = he/she/it proceeds

Since pompa is a singular subject, Latin uses procedit: the procession proceeds.

Latin does not have articles like English the and a/an.

So a noun like dies or pompa can mean:

• the day or a day
• the procession or a procession

You figure out which is meant from the context.

That is why:

• Dies sollemnis est could be understood as The day is festive
• longa pompa per forum procedit could be a long procession proceeds through the forum or the long procession proceeds through the forum

English has to choose an article; Latin usually does not.

Latin word order is much freer than English word order because the endings show how words function.

So this sentence could be rearranged in various ways without changing the basic meaning, for example:

• Longa pompa per forum procedit
• Per forum longa pompa procedit
• Pompa longa per forum procedit

The original order is natural and clear, but Latin often changes word order for emphasis, style, or rhythm.

For a learner, the important thing is to track the endings, not just the position.

It can have a somewhat stronger or more formal sense than plain English festive.

Sollemnis can suggest something like:

• ceremonial
• ritual
• customary in a formal or sacred way
• solemnly observed

So dies sollemnis is not just a day when people are happy; it is often a day marked by official, religious, or traditional observance.

That fits well with the second clause about a procession moving through the forum.