The earliest burial places of the Old Kingdom Egyptian nobiility were called , flat-topped one-story rectangular buildings with slanted walls.

Mastabas

Explanation:

The earliest burial places of the Old Kingdom Egyptian called Mastabas. Mastabas were constructed in a flat-topped one-story building in a rectangular shape with sloping sides as a burial ground for the royalty. These burial structures were built with mud bricks and later with stones. The structure constructed with an underground burial chamber along with storage chambers to stock materials and food for the afterlife.    

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an informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.