Filoli was built between 1915 and 1917 for William Bowers Bourn II, owner of one of California's richest gold mines and president of Spring Valley Water Company, supplying San Francisco's water, and his wife, Agnes Moody Bourn. They wanted a country estate nearer to their home in San Francisco. The principal designer, San Francisco architect Willis Polk, used a free Georgian style that incorporated the tiled roofs characteristic of California. Polk had previously designed Bourn's houses in Grass Valley and on Webster Street in San Francisco. Polk's friend, artist and designer Bruce Porter was commissioned to collaborate with the Bourns in planning the gardens, which were laid out between 1917 and 1922. The horticulturist who designed the plantings and fixed the original color schemes was Isabella Worn; she supervised the garden's maintenance for 35 years.