It's important to remember Celtic culture isn't uniform. There are enormous regional differences in culture between various Celtic peoples. However despite the differences, the cultures can clearly be traced back to their Hallstatt roots. As the Celtic culture dispersed and it's people migrated from it's origin point in central Europe, the culture evolved gradually. For example, Celtic culture as found in Ireland is very different from Celtic culture in Anatolia, but as both cultures originated and can be traced back to their roots in central Europe, it becomes obvious that they are of the same overall cultural origin. It is also worth noting that, despite all the differences that evolved between the various Celtic groups, many aspects of their culture did remain similar. Celtic culture was often very different from that of their non-Celtic neighbours, so often a Celtic group in Eastern Europe might have more cultural similarities with a Celtic group in Western Europe than with a non-Celtic group who lived right beside them.