https://www.geldersarchief.nl/bronnen/archieven/?mivast=37&mizig=210&miadt=37&miaet=1&micode=0908&minr=28311247&miview=inv2

Link met Wolter Berck?
https://www.google.nl/books/edition/Die_Ratinger_Edelherren_und_ihre_Burg/lREBAAAAMAAJ?hl=nl&gbpv=1&bsq=%22wolter%20berck%22&dq=%22wolter%20berck%22%20-cologne%20-holbein&printsec=frontcover