Analysis of information sources in references of the Wikipedia article "Gevangenpoort" in English language version.
He [Cornelius De Witt] was confined in the Gevangenpoort, and his brother [John de Witt] came to visit him in the prison. A vast crowd on hearing this collected outside, and finally burst into the prison, seized the two brothers and literally tore them to pieces. Their mangled remains were hung up by the feet to a lamp-post. Thus perished, by the savage act of an infuriated mob, one of the greatest statesmen of his age.
The Nieuwe Kerk, or new church (first half 17th century), contains the tombs of the brothers De Witt and of the philosopher Spinoza.
