Where did the bricks at My Son come from?

I went to My Son ruins, which are close to Da Nang in Vietnam. It's convenient to take a taxi from the airport. It costs about 4,000 yen round trip. A short walk from the entrance is the electric cart stand, so you can ride it into the interior. Once you arrive, you can walk around the whole area. An hour is enough to see everything. The ruins are similar to the pagodas in Bagan, Myanmar, but most of them have collapsed. These ruins are also made of bricks, but I couldn't find any information on where the bricks were made. I'll look into it the next time I visit.