Vobis per has scalas lente eundum est, quia gradus alti sunt.

Eundum est is the gerundive of obligation (also called the passive periphrastic). It expresses necessity: it must be gone = more naturally, you must go.

With ire (to go), Latin often uses this construction to say that someone has to go somewhere:

• mihi eundum est = I must go
• vobis eundum est = you must go

Latin could also say ire debetis, but eundum est is a very common and idiomatic way to express obligation.

In this construction, the person who has the obligation is put in the dative.

So:

• vobis eundum est = literally, to you, it must be gone
• idiomatically, you must go

This is often called the dative of agent with the gerundive of obligation.

Compare:

• mihi legendus est liber = I must read the book
• nobis laborandum est = we must work

So vobis does not mean the subject in the usual English sense; it marks the people on whom the necessity rests.

Because this is an impersonal use of the gerundive.

The verb ire is intransitive: it does not take a direct object. With intransitive verbs, the gerundive of obligation is usually used in the neuter singular, regardless of who must do the action:

• mihi currendum est = I must run
• vobis eundum est = you must go

So eundum is not agreeing with vobis. It is the fixed neuter singular form used in this impersonal construction.

It is the gerundive of eo, ire (to go), and this verb is irregular.

Its gerundive is:

• eundus, eunda, eundum

So:

• eundum est = it must be gone / one must go

Because ire is irregular, its forms can look surprising:

• infinitive: ire
• present participle: iens
• gerundive: eundus

So yes, eundum really does belong to ire.

Because per takes the accusative case, and scalas is feminine plural accusative.

So:

• scalae = nominative plural
• scalas = accusative plural
• has = feminine plural accusative of hic, haec, hoc (this)

That is why Latin says:

• per has scalas

not:

• per hae scalae
• per his scalas

The forms have to match both the noun and the preposition.

Here per means something like through, along, or by way of.

With a route or passage, per often indicates the path taken:

• per viam = along the road / by way of the road
• per portam = through the gate
• per has scalas = by way of these stairs / along these stairs

In natural English, we often would not translate it very literally. Depending on context, English might say:

• on these stairs
• by these stairs
• down these stairs
• up these stairs

But the Latin idea is that the movement happens via these stairs.

Latin often uses scalae in the plural for a flight of stairs or staircase, just as English says stairs rather than a stair when we mean the whole set.

So:

• scalae / scalas = stairs, staircase

This is very natural in Latin. A learner should get used to some nouns being commonly used in the plural when English also tends to use a plural form.

They are related, but not identical.

• scalae / scalas refers to the staircase or flight of stairs as a whole
• gradus refers to the individual steps

So the sentence distinguishes between:

• the stairs you are going on: per has scalas
• the steps being high: gradus alti sunt

A very natural sense is:

• You must go slowly on these stairs, because the steps are high.

Because gradus is a masculine noun.

It belongs to the fourth declension:

• singular: gradus
• plural nominative: gradus

Since gradus here is nominative plural and masculine, the adjective must agree with it:

• gradus alti sunt = the steps are high

So:

• alti = masculine plural
• not alta, which would be neuter plural

The verb tells you.

• sunt = are, so the subject must be plural
• therefore gradus here is nominative plural

This is useful because fourth-declension forms can look ambiguous. The ending -us can be singular or plural in different contexts, so you often have to use the rest of the sentence to decide.

Here:

• gradus alti sunt = the steps are high not
• the step is high

It is an adverb, meaning slowly.

It comes from lentus, -a, -um (slow), and the adverb is:

• lente = slowly

It modifies the verbal idea in eundum est:

• lente eundum est = one must go slowly

It is not describing a noun, so an adjective would not work here.

Because quia here introduces a straightforward factual reason:

• because the steps are high

Latin normally uses the indicative after quia when the cause is being presented as a fact:

• quia gradus alti sunt

If the writer were presenting someone else’s supposed reason or a more indirect idea, other constructions can appear in Latin, but the indicative is the normal choice here.

Latin word order is much more flexible than English word order because case endings show the grammatical relationships.

So vobis can be placed first for emphasis:

• Vobis ... eundum est = you are the ones who have to go

A Roman could rearrange parts of the sentence without changing the basic meaning, though some orders sound more natural than others. This sentence puts:

• vobis early, to mark who has the obligation
• lente near eundum est, because it modifies the action
• quia gradus alti sunt at the end, as the reason

So the order is not random, but it is more flexible than in English.