Islam initially spread during the seventh century, initially rooting itself in modern day Ethiopia before expanding into Egypt. From there, Islam was spread by Muslim warriors and traders making their way west towards Morocco, eventually installing Arab rule that would convert the majority of Northern Africa to Islam. Familiar with sailing due to their origin in the Arabian Peninsula, Muslims sailed down the Nile and the East African coast, planting the seeds for what would be a more gradual transition to Islam. As Muslims settled along Saharan trade routes, they established settlements in Western and North Central Africa. The slave trade eventually resulted in the establishment of Muslim societies in South Africa as well. Where Islam became rooted in culture, mosques were built, often exhibiting architectural fusion between traditional Muslim construction and that of the native African (most notably Berber) peoples.