The seaport of Dunkirk had for many years been a nest of pirates, who preyed upon Dutch commerce in the narrow seas.

The States-General, urged on by Oldenbarneveldt, resolved in the spring of 1606 to despatch an expedition to besiege and capture Dunkirk.

Both Maurice and William Lewis were opposed to the project, which they regarded as rash and risky.

The States-General, however, hearing reports of the archduke's soldiery being mutinous for lack of pay, persisted in their purpose, and Maurice, against his better judgment, acquiesced.

A body of picked troops, 12,000 foot and 3000 horse, was assembled on the island of Walcheren.