It's a photo of the irrepressible will of life. It reminds me of the Netherlands' motto, "Je Maintiendrai," meaning something to the effect of "I will keep on."
Also, it represents nature's inevitable reclaiming of structures built by people. Even stone walls eventually succumb to tiny roots and weather.
Still, you have to admire the stone mason's work. The rocks fit together as tightly as any jigsaw puzzle.
