On Wikipedia it is stated that
The meridan of Antwerp is one of several prime meridians that have been used for geographic referencing. It is running through the city of Antwerp, in Flanders, Belgium, and forming the 0° longitude upon which some Belgian maps were based. This is also where Gerardus Mercator published the first modern atlas, Theatrum Orbis Terrarum, first printed in 1570.
I couldn't however find any reference backing this. On the image on Wikipedia itself the prime meridian seems to be based in the middle of the atlantic.
