Learn Farsi: تقریباً ده یادبود در این میدان قرار دارد. - Approximately ten monuments are located in this square.

In Farsi, when the subject is inanimate (like یادبود, meaning "monument") and plural or quantified by a number, the verb is usually kept in the singular form. If the subject were animate (like "ten tourists"), you would use a plural verb instead.

Why isn't the plural marker -ها used on یادبود after the number ده?

In Farsi, whenever a noun is immediately preceded by a specific number, the noun itself must remain in the singular form. You say ده یادبود (literally "ten monument"), never ده یادبودها.

How would I apply this lesson's superlative partitive grammar to say "Ten of the most famous monuments are located in this square"?

You would use the preposition از (of/from) and a superlative adjective: ده تا از معروف‌ترین یادبودها در این میدان قرار دارد. Notice that in this partitive construction, یادبود takes the plural suffix -ها because it is part of a larger group being selected from, rather than directly following the number.

Could I just use است or هست instead of the compound verb قرار دارد here?

Yes, you could say تقریباً ده یادبود در این میدان هست to mean "There are about ten monuments in this square." However, قرار دارد (from قرار داشتن, meaning "to be located" or "situated") is slightly more formal and sounds very natural when describing the geographic placement of landmarks, buildings, or cities.