Question

Novgorod was the main Russian port for many centuries and was important for Baltic Sea trade. Объясните наличие артиклей

Answer 1

Тут только один артикль - 
the main - это устойчивое выражение. main всегда употребляется с the
например: the main idea, the main city.

Answer 2

Артикль the.
the main является устойчивым выражением, т.е. main всегда употребляется с the.

Answer 3

In the sentence "Novgorod was the main Russian port for many centuries and was important for Baltic Sea trade," the definite article "the" is used before "main Russian port" and "Baltic Sea trade."

The use of the definite article "the" before "main Russian port" indicates that the sentence is referring to a specific port, namely, Novgorod, which was the main port in Russia during the time period being discussed.

Similarly, the use of the definite article "the" before "Baltic Sea trade" indicates that the sentence is referring to a specific type of trade, namely, the trade that took place on the Baltic Sea, of which Novgorod played an important role.

Overall, the use of the definite article "the" helps to specify which particular port and type of trade are being discussed in the sentence.