The Sacred Field is a Building that only the Indians can create. It has the ability to build Sacred Cows for 100 food, which gather experience, and gather even faster when tasked to a Sacred Field.
The Sacred field can have 10 gatherers at a time, but can build up to 20 Sacred Cows, so to get full benefit of the experience gain, 2 Sacred Fields are needed. Sacred Fields are good at earning shipments quickly, which is a big benefit if you are in Industrial Age and want to use the infinite use Urumi Swordsmen card.