Celtic tribes lived in what is present day Croatia during the time of Christ. Today there are some estimates that 18% of Croats are of that old Celtic descent. Art and cultural designs indicate who influenced who.

I find the similarity of the Celtic Weave and Celtic Cross to be quite similar to the traditional Croatian Cross which is based on the Cross on the Baptismal Font of Croatian Duke Viseslav circa 9th century AD.

This is the Croatian Weave Cross


The most striking resemblance to Celtic design is found in this Celtic wedding ring showing three strand weave



Celtic crosses interestingly have a weave patter inside the cross.
On the left is a basic and on right more ornate Celtic weave Cross



2,500 years ago, prior to the invasion by the Roman Empire, the present day city of Sisak was the Celtic city named Segestica. Under Roman rule the name changed to Siscia. Belgrade was the Celtic city of Singidunum.