Book excerpt: A sprawling megacity of nearly twenty million people, Delhi has forgotten its ecological history, a key part of which is the Ridge, often referred to as Delhi's 'green lung'. At various points, Delhi has been a crucial hub of politics, warfare, trade and religious expansion on regional and global levels. Placing Delhi's environment at the front and centre of its unique history, the book tells the tale of the Ridge, which resonates far beyond the boundaries of India's capital. The Ridge offers a crucial vantage point for viewing these historical and geographical interconnections. Its trees can't be separated from the stones below them, nor the cities that rose and fell around them. Only with this perspective does a clear picture of the Ridge - and Delhi as a whole - emerge.