Novo Brdo was a metropolis at the time, with a huge medieval fortress built on the top of an extinct volcano cone, the remains of which can be visited today, and residential sections sprawling all around. In the outer wall of the fortress a large cross is visible, built into the stones. The castle, or fortress, was thought at one point to have dated back to the time of the Serbian Empire. The population at its height was estimated to exceed 5,000 people. At the first half of 15th century, Serbian Orthodox bishops of Lipljan resided in Novo Brdo. There were mines and smelting furnaces for iron, lead, gold and silver ores. Novo Brdo silver is known by its glam silver (argentum de glama, an alloy of silver with 1/6-1/3 gold). In 1450 the mines of Novo Brdo were producing about 6,000 kg of silver per year. The medieval settlement was an important producer of Serbian pottery and other goods.