If you talk about that era (6th-7th century India) there are at least 2 mathematicians who will be counted among the greatest ever in that highly competitive field. By greatest ever I mean in the same breath as Gauss, Newton, Euler, Ramanujan, Fermat.
Aryabhata
Brahmagupta
Even Panini (1000 years before the Guptas, from Gandhara, modern day Khyber Pakhtunkhwa province [MENTION=131701]Mamoon[/MENTION]) wasn't just a grammarian
Fast forward to 12th century and we also have Madhava and Bhaskaracharya.
Their inventions weren't trivial, legends like Gauss, Galois, Leibniz have taken inspiration from their body of work, carried forward their mathematical theorems and methods.
These weren't the only ancient mathematicians, we can not underplay the significance of scholars from that era just because some University professor can crack them today, today's greats stand on the shoulders of giants of that era.
Chess (Chaturanga) was invented in the Guptan age, but the game has evolved and become almost unrecognizable today. Doesn't mean we underrate the pioneers. What if I told you there were puzzles which couldn't be solved by the best of humanity for 1000 years? Since I was talking about the Islamic Golden Age in my previous post a while back allow me to present an interesting piece of information. A few years ago I came across the profile of an Arab (or Persian/Turkic, unsure of origin) chess player from the 9th century, Abu Bakr bin Yahya al-Suli who was employed in the services of the Caliph of Baghdad. A legendary player of shatranj (different rules compared to modern day chess) in that era who used to give blindfold simuls. He wrote the Kitab Al-Shitranj dealing with chess strategy and one of the more important historical sources on the early history of chess. It had a problem known as 'Al-Suli’s Diamond', a puzzle that went unsolved for more than 1000 years. The problem was cracked by Soviet GM Yuri Averbakh in the 1980s. And this wasn't the only such puzzle which eluded many for centuries, there are other examples from other empires including Indian ones. If you give me a choice to live a princely life in the Mughal era or as a commoner in the services of Al-Suli I would choose the latter, that is the kind of legacy that attracts me.
Similarly in mathematics quite a few inventions made in 6th century engaged the best of minds for over a millennium. Today those concepts are covered in UG maths courses or even high school (eg Archimedes, Euclid) but that doesn't diminish the greatness of our predecessors who didn't have tools and knowledge base we have today a button click away.