Debated. Two old churches stood in the port of Adulis.
Adulis is on the Red Sea coast of Eritrea. It belonged to the Kingdom of Aksum. That kingdom turned to Christianity in the 4th century AD, after King Ezana took the throne in 320 AD. Tests on the ruins date the larger church to between 400 and 535. It would have been a cathedral near the middle of the city, with a place for baptism. The smaller church dates to between 480 and 625. It was round, with a dome for a roof, in the eastern part of the city. The capital, Aksum, was about 160 kilometres inland.
The page says the look of the churches may show local choices, not an order from the king.
https://www.ancient-origins.net/news-history-archaeology/aksumite-churches-0017633