If "Der Ring des Nibelungen" is the high-water mark of opera (which it is) and opera is the high-water mark of Western art (which, per Gesamtkunstwerk, it is), then Richard Wagner's Ring Cycle stands as the high-water mark of Western art as such.
Image is a photograph of the Rhinemaidens from the Bayreuth premiere in 1876.
I'm actually optimistic about civilization's revival later in the 21st century and beyond; we're in the earliest stages now. But like classical antiquity before it the Long 19th Century stands as the high-water mark, daring its successors to widen their horizons and go further.
Image is "Siegfried leaves Brünnhilde in search of adventure" by Arthur Rackham (1911).
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