Original: Edo consequently rapidly grew from what had been a small, virtually unknown fishing village in 1457 to a metropolis with an estimated population of 1,000,000 by 1721, the largest city in the world at the time.
Simplified: Edo consequently rapidly grew from what had been a small, virtually unknown fishing village in 1457 to a big city of 1,000,000 residents by 1721, the largest city in the world at the time.