One does not need to look at ancient civilisations for unknown technologies. If you are somewhat interested in the history of technology, one will quickly see

One does not need to look at ancient civilisations for unknown technologies. If you are somewhat interested in the history of technology, one will quickly see many examples since the mid 19th century of technologies that came into existence and are no more. Due to the way technological development flows, once a particular technology disappears, it can be difficult if not impossible to duplicate it even 20 to 30 years later. If one reads fiction from the forties, you will find references to specific types of technology (especially in the space opera genre) that were in existence at that time and were highly advanced for that time. Yet, different types of technology have replaced those kinds in the years that followed and onto today. There is much we do not know about how things were done in past centuries and, surprisingly, we cannot duplicate those crafts today. We don't have the required technology. Yet there are nanotechnologists who are actively studying to duplicate those century old unknown today processes.