Architectus plumbum ad molem portat.

Because architectus is in the nominative singular, the case normally used for the subject of a finite verb.

In this sentence:

• architectus = the architect / an architect
• portat = carries

So architectus is the one doing the carrying.

The ending -us is a very common nominative singular ending for second-declension masculine nouns.

Here plumbum is the direct object, the thing being carried, so it is in the accusative singular.

For many second-declension neuter nouns, the nominative singular and accusative singular are both -um. So:

• plumbum can mean lead as a dictionary form
• and in this sentence it is also the accusative form, lead as the thing carried

A learner should notice that neuter nouns often have the same form in the nominative and accusative singular.

Molem is accusative singular.

It appears after the preposition ad, and ad normally takes the accusative when it means to, toward, or up to.

So:

• ad molem = to the structure / to the mass / toward the barrier
  depending on the meaning of moles in context

The important grammar point is:

• ad
  • accusative = motion toward something

Because ad shows direction toward a place or goal.

Compare the roles:

• plumbum = what is being carried
• ad molem = where it is being carried to

Without ad, molem would just look like another accusative noun, and the sentence would be less clear. Ad tells you this noun is part of a prepositional phrase of motion, not another direct object.

Portat is:

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

from the verb porto, portare = to carry

So portat means:

• he carries
• she carries
• it carries

In this sentence, since the subject is architectus, it means the architect carries.

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

So:

• architectus can mean the architect or an architect
• plumbum can mean the lead or just lead
• molem can mean the structure or a structure

You decide from context which English article sounds natural.

Latin word order is more flexible than English word order because the endings show the grammatical roles.

So Architectus plumbum ad molem portat means the same basic thing as:

• Plumbum architectus ad molem portat
• Ad molem architectus plumbum portat

as long as the forms stay the same.

That said, the given order is quite natural:

• architectus — subject first
• plumbum — object next
• ad molem — destination
• portat — verb at the end

Putting the verb at the end is very common in Latin prose.

The dictionary form is moles.

More fully, you might see it listed as:

• moles, molis — a third-declension feminine noun

In the sentence, molem is the accusative singular form.

So the pattern is:

• nominative singular: moles
• accusative singular: molem

Its basic meaning is lead, the metal.

In many contexts, especially Roman ones, plumbum can refer to actual lead used for practical purposes such as:

• weights
• pipes
• building materials

So in this sentence, it probably means the architect is carrying lead as material, not just some abstract object.

Usually yes, but with an ancient nuance.

In Latin, architectus refers to a master builder, designer, or architect. In Roman context, the role could overlap more with what English might call:

• architect
• builder
• engineer

So architect is a good translation, but it may suggest a somewhat broader practical role than the modern profession.

In this sentence it is singular because the form is molem, the accusative singular.

If it were plural, the form would be different. For this noun, the accusative plural would be moles.

So:

• ad molem = to the structure / mass
• ad moles = to the structures / masses

The same principle applies to other nouns in Latin: singular and plural are shown by endings.

A good breakdown is:

• Architectus — subject, nominative singular
• plumbum — direct object, accusative singular
• ad molem — prepositional phrase showing direction, ad
  • accusative
• portat — verb, 3rd person singular present active

So the structure is:

subject + object + destination + verb

That is a very useful pattern to recognize in simple Latin sentences.