It started with a few people building a home in Williamsburg in 1897. And over the past 125 years, the firm that came to be known as D.A. Sullivan & Sons Inc. has expanded in every way a construction firm can. Its vast portfolio of projects includes construction and renovation of schools, libraries, hospital facilities, dormitories, churches, and much more. While there are many keys to the success of the firm, it’s fourth-generation president says it all comes down to relationship-building.