The castle of Vredenburg had been built by emperor Charles V after annexing Utrecht in 1528, and was manned by a Spanish garrison.
The Dutch rebels besieged the Vredenburg fortress and, following negotiations, the garrison abandoned the castle in February 1577.
Trijn van Leemput is said to have gathered a large group of women and marched on the castle, carrying a makeshift banner made out of a blue apron tied to a broom.
She and her husband, brewer and miller Jan Jacob van Leemput, moved into a large house on the Oudegracht canal in Utrecht in 1555.
Trijn's husband was a guild leader and member of the city government, and was one of the four deputies who negotiated with William the Silent on the conditions for Utrecht's entry into the Pacification of Ghent, the Dutch coalition against Spain.