The town of Tvarditza has a population of 6 000 inhabitants and lies at a distance of 46 km northwest of Sliven. Tvarditza is a municipal centre with 9 component settlements. The Balkan coal pool, occupying the central part of the Stara Planina Mountains between Gabrovo and Sliven, is located in the region of Tvarditza. There are remains from the Neolith, an ancient settlement and a medieval fortress in the region of Tvarditza. The town is mentioned in the Ottoman documents from 1472 under the name of Ferdidzhi Kyuberan. More about 'Sliven district' : The town of Sliven The town of Nova Zagora The town of Kotel The town of Shivachevo The town of Kermen Protected territories - Sliven