However scholars claim that the power of the Sultante of Brunei was at its peak between the 15th and 17th centuries, with its power extending from northern Borneo to the southern Philippines. By the 16th century, Islam was firmly rooted in Brunei, and the country had built one of its biggest mosques. In 1578 Alonso Beltran a Spanish traveller described it as being five stories tall and built on the water.