Complex sentence: Under his reign Christianity gained a strong foothold in the country, with many churches built in Mbanza, of which the Kulumbimbi Cathedral (erected between 1491 and 1534) was the most impressive.
Split into simpler sentences: Under his reign Christianity gained a strong foothold in the country. Many churches were built in Mbanza, of which the Kulumbimbi Cathedral (erected between 1491 and 1534) was the most impressive.