For too long we have placed ourselves outside of nature, forgetting that we respond to the same fundamental factors that control the expansion of other species. We have conceived the place where we live as something separate from the rest of nature, against nature. This is why a significant part of our chances of survival will depend on how we imagine our cities in the coming years. Our urban success requires, in fact, a continuous and exponentially growing flow of resources and energy, which however are not unlimited. Furthermore, crucially, global warming can definitively change the environment of our cities and constitute precisely that fatal mutation of the conditions on which our survival depends. This is why it has become vital to bring nature back into our habitat. The cities of the future, whether built ex novo or renovated, must transform themselves into phytopolis, places where the relationship between plants and animals comes closer to the harmonious relationship we find in nature. There is nothing of greater importance than this for the future of humanity.