Rapid strides were made in astronomy during this period. Aryabhata and Varahamihira were two great astronomers and mathematicians. Aryabhata stated that the earth moved round the sun and rotated on its own axis. Aryabhata, who is believed to be the first to come up with the concept of zero, postulated the theory that the Earth moves round the Sun, and studied solar and lunar eclipses. Aryabhata's most famous work was "Aryabhatiya". Varahamihira's most important contributions are the encyclopaedic Brihat-Samhita and "Pancha-Siddhantika" (""). Metallurgy also made rapid strides. The proof can be seen in the Iron Pillar of Vaishali and near Mehrauli on the outskirts of Delhi, which was brought from Bihar.