Write a question about the following article: Louis arrived in Charleroi on 5 May 1672. Turenne's 50,000 men set off on 11 May. Arrived at Visé, Louis decided not to lay siege to Maastricht but only to occupy the surrounding forts of Tongeren, Maaseik and Valkenburg so its garrison stayed bottled up. Moving along the Rhine, Rheinberg, Wesel, Burick and Orsoy were taken. Turenne then took Nijmegen , with 4,000 infantry and 400 cavalry, and from there Fort Crèvecœur near 's-Hertogenbosch, which fell after only two days. In view of these defeats, the Dutch public panicked and rioted. Leading politicians Johan and Cornelis de Witt were lynched by an angry Orangist mob, following rumours  that they were planning the assassination of William of Nassau . On 4 July, William was acclaimed stadtholder. As the French had promised the major cities of Holland to the English, they were in no hurry to capture them. The French tried to gain sixteen million guilders from the Dutch in exchange for a separate peace. This demand and other conditions posed by the French stiffened Dutch resistance. Negotiations gave the Republic time to finish the inundations along the Dutch Water Line, started on 22 June 1672. Luxembourg laid siege to Groningen but failed to take it. An attempt was made to invade the Republic by sea; this was thwarted by Admiral Michiel de Ruyter in four strategic victories against the combined Anglo-French fleet . The first of these naval victories was the Battle of Solebay.

Question about the article:
How many forts surrounded Maastricht?