The A-Group culture vanished, followed later by the C-Group culture (2400–1550 BCE). Settlements consisted of round structures with stone floors. Structural frame was achieved with wooden or pliant materials. Mudbricks became the preferred building materials as settlements became larger. Graves were circular cylindrical superstructures made of stoned wall. The pit was filled with gravel and stones, and covered with dried mud roof or hay roof. Later, during the Second Intermediate Period of Egypt (circa 1650 to 1550 BCE), an adobe chapel was placed to the north of the grave. Graves were from El Ghaba, Kadero, Sayala, and various other sites in northern Sudan.