This is the 5476th most frequent Korean word.
많았다고
"많았다고" means "said (that there) was a lot" or "was abundant," in a past context.
The word '많았다고' here is used to report a past state or situation where there were many friends, often used in indirect reported speech.
그는 친구가 많았다고 말했다.
He said that he had many friends.
In this sentence, '많았다고' serves to describe the quantity of students in the past, and is again referencing a recalled state.
교실에는 학생이 많았다고 회상했다.
He recalled that there were many students in the classroom.
Here, '많았다고' is used to indicate information regarding a past situation relayed through hearsay or reporting.