§ Valaquenta The Silmarillion

Then those of the Ainur who desired it arose and entered into the World at the beginning of Time; and it was their task to achieve it, and by their labours to fulfil the vision which they had seen. Long they laboured in the regions of Eä, which are vast beyond the thought of Elves and Men, until in the time appointed was made Arda, the Kingdom of Earth. Then they put on the raiment of Earth and descended into it, and dwelt therein.