Most scholars place the Rigveda between the twelfth and ninth centuries BC. Since the text mentions several metals except iron, the inference might be drawn that the Rigveda was composed before the dawn of the Iron Age. It could be a Bronze Age text. The manufacturing of iron began in the northern part of the Indian subcontinent, the geographical area of the Rigveda, between the twelfth and tenth centuries BC. The work on the Rigveda could have started earlier than the twelfth century BC, perhaps between the fourteenth and tenth centuries BC, or even in the second half of the second millennium BC. The rich tradition of Vedic gods, rituals, mythologies, cosmological queries, and the linguistic and poetic conventions on which the Rigveda has been developed would have to predate the text by a number of centuries and could even have originated in the third millennium BC. On astronomical grounds, which assume that the ancient Hindus had the ability to chart the sun’s course, some scholars (noted by Arthur Anthony Macdonell in his 1917 book A Vedic Reader for Students) have placed the oldest Rigveda hymns as far back as the sixth millennium BC.