Abstract: Currently we are working on a translation into English, plus commentary, of Ludolph van Ceulen's book "Vanden Circkel" ("On the circle"), originally published in 1596. Through a number of examples I will show why such a translation is of interest to a modern mathematician and/or historian of mathematics: partly because the book falls in with the tradition of mathematical practice at the time, partly because it contributes to reshaping that tradition, and partly because it contains some very advanced results (to 16th century standards). There is even a kind of "open problem": in specific instances we still do not know the computational methods that Van Ceulen applied.
