The Sierra Madre, Filipinos will tell you, is the backbone of Luzon, the main island of the country. Some even describe the mountain as their mother and protector. Stretching for more than 500km (310 miles) from north to south, her uneven, rugged peaks are thought to shield the 64 million people who live there, including those in the capital Manila, from the worst of the strong typhoons which barrel in from the Pacific Ocean.