The Mongol invasion of 1241 prompted a surge in military construction in Transylvania, with wood and earthen defenses abandoned in favor of stone, assembled in haste and without much initial attention to artistic detail. At Câlnic, the fortress began as a residence for a Graf (count), one of the last such to be built in Transylvania. Around 1270, the nobleman Chyl of Kelling, whose family gave the village its German name, built a keep for his residence. The strong parallelepiped structure, with a ground floor and three floors for living space, came to be known as the Siegfried tower. Frequent Ottoman attacks led the keep to be fortified with a defensive level and surrounded by a massive wall. The oval precinct around the keep was fitted with a guard tower to the south and a gate tower to the north. The structure was surrounded by a water-filled moat, with access only by drawbridge. The noble owners never went along very well with the local notables, and in 1430, the final Graf sold the fortress to the villagers and moved out.