cornerstones

noun

1. 1

   A stone forming the base at the corner of a building.

2. 2

   Such a stone used ceremonially, often inscribed with the architect's and owner's names, dates and other details.

   “The cornerstone on the Flatiron Building is set on the Fifth Avenue facade.”

3. 3

   That which is prominent, fundamental, noteworthy, or central.

   “Exceptional service is the cornerstone of the hospitality industry.”