Complex sentence: Raynald laid siege the Egyptian fortress on Ile de Graye while part of his fleet made a plundering raid along the coasts, threatening the security of the holy cities of Mecca and Medina.
Split into simpler sentences: Raynald laid siege the Egyptian fortress on Ile de Graye. Part of his fleet made a plundering raid along the coasts, threatening the security of the holy cities of Mecca and Medina.