The Onze-Lieve-Vrouwetore is a church tower in Amersfoort. The Late Gothic building is 98.33 metres (322 ft 7 in) tall and reaches high above the inner city. It is one of the most eye-catching monuments in town and the third highest church tower in the Netherlands. The nickname of the tower is Lange Jan (‘Long John’). The church that belonged to the tower was destroyed by a gunpowder explosion in the 18th century.

With a height of over 98 meters, the Onze Lieve Vrouwetoren is the third highest late medieval tower in the Netherlands. The pride of Amersfoort is the most famous eye-catcher in the city and is also called Lange Jan. The location of the tower is the cadastral zero point of the Netherlands.

he first chapel on site was constructed on this site in the 14th century. In the 15th century the chapel was replaced by new church with three aisles. When the tower was built is not exactly known. Construction started around 1444 and was finished around 1470. The official documents of the construction were destroyed by the Protestants in 1579 during the reformation and the ensuing iconoclasm. The church and tower were taken over by the Protestants and no longer belonged to the Catholics.

The church also has been used for other purposes than worshiping. It was used as a storage place for ammunition and as laboratory for the manufacturing of shells.

In 1986 some research was done into its history and in the current square one can see the original plan of the church. The spire of the church burned down in 1651 and again in 1804. The tower was restored in 1912–1932, in 1965–1970 and in 1993–1996.