Examples are universities, hospitals, large corporations, etc. They are in high demand and can rather easily get jobs elsewhere. The most important requirement for employees in this culture is to fit into the group. Usually employees start at the bottom and stay with the organization. The organization promotes from within and highly values seniority.
Examples are the military, some law firms, etc.
Fortress Culture Employees don't know if they'll be laid off or not. These organizations often undergo massive reorganization. There are many opportunities for those with timely, specialized skills. Examples are savings and loans, large car companies, etc.