Farnese finally laid siege to the great seaport of Antwerp. The town was open to the sea, strongly fortified, and well defended under the leadership of Marnix van St. Aldegonde. Farnese cut off all access to the sea by constructing a bridge of boats across the Scheldt. Antwerp surrendered in 1585 as 60,000 citizens (60 per cent of the pre-siege population) fled north. All of the southern Netherlands was once more under Spanish control.