
Abrahah was the governor of Yemen, appointed by Najaashi (Negus), the emperor of Abyssinia. When he noticed all the Arabs travelling to Makkah Mukarramah to perform Tawaaf of the Baitullah, he decided to erect a magnificent, highly decorated structure in the name of Christianity so that the Arabs would abandon the simple Ka‘bah and make Tawaaf of his fake Ka‘bah. He therefore erected a beautiful church in the capital city of San‘aa.
(Extracted from Seeratul Mustafa 1/46)