영어 문장 구조와 해석 부탁드려요

“He said that one section included mosques, built by the Islamic people who dwelled there.”에서 built 이하가 mosques를 꾸미는 건지 궁금해요.
“Attending his reading, he said, were large numbers of Hispanic people, forty thousand of whom lived in the same city.”도 정확한 해석을 부탁드려요.
특히 attending his reading 부분이 잘 이해되지 않네요.