Indian classical music is one of the oldest musical traditions in the world. The Indus Valley civilization has sculptures that show dance and old musical instruments, like the seven holed flute. Various types of stringed instruments and drums have been recovered from Harappa and Mohenjo Daro by excavations carried out by Sir Mortimer Wheeler. The Rigveda has elements of present Indian music, with a musical notation to denote the metre and the mode of chanting. Indian classical music (marga) is monophonic, and based on a single melody line or raga rhythmically organized through talas. "Silappadhikaram" by Ilango Adigal provides information about how new scales can be formed by modal shifting of the tonic from an existing scale. Present day Hindi music was influenced by Persian traditional music and Afghan Mughals. Carnatic music, popular in the southern states, is largely devotional; the majority of the songs are addressed to the Hindu deities. There are also many songs emphasising love and other social issues.