Another good webste is Knots on the Web which has information about all kinds of knots and many links to other sites. This ancient book is now kept in Trinity College Library in Dublin. This type of design has been studied by many people. Some people like Celtic Knots for artistic reasons, others are fascinated by the mathematics of the designs. More pictures can be found at Book of Kells Images .
Many Celtic knots are continuous - as if they are made from one long piece of string.
So they are 'mathematical' knots. So these are 'links' of mathematical knots. More information can be found at the Celtic Knots website . We also have a good article on our website called Links and Knots . You can make your own Celtic Knots by using five basic design tiles.