This is an illustration of a model of a paradox – they hydrostatic paradox, as demonstrated by Blaise Pascal. The paradox is that the pressure at the bottom of a column of water only depends on the height of the water, not the shape or the volume. Six tons of water and six ounces of water will exert the same pressure if they’re each in a vessel that’s only a foot tall.
And, if you connect any vessels together, regardless of their shape, they’ll fill with water up to the same level. The big vessel won’t force water further up the small one. Seems weird. There’s a better explanation of what’s happening here.
Max Kohl’s engraving I found on Wikimedia Commons.