Why was the globe theatre that shape?

Answer 1

The shape of the open-air playhouses in Elizabethan London was based on the structure of innyards. Before there were purpose-built Theatres, travelling players would set up in the yards of inns which were enclosed courtyards with one doorway and balconies from the rooms. A stage would be built at one end. This arrangement had a number of advantages--the single door allowed the players to control admission, the open-air structure enabled them to use natural light, the balconies provided excellent viewing for some, but many more could watch from the ground floor.

Purpose-built playhouses beginning with the Theatre in 1576 (which we know was built on the same plan as The Globe because the Globe was built from the timbers taken from the Theatre when it was torn down) incorporated these features of innyards: controlled entrances, balconies and a standing-room floor, and an open roof for lighting. The main difference was that the playhouses were polygonal (the Globe had 20 sides) rather than rectangular so that all the balcony seats were "good seats".