The asses' bridge, or pons asinorum is generally accepted as being the 5th proposition in Euclid's first book, which states that the angles at the base of an isosceles triangle are equal to one another. According to Brewer's Dictionary of Phrase and Fable, the reason it came to be known as the pons asinorum is that this was the first theorem that gave boys (girls did not do mathematics in the old days) trouble understanding. Some sources state that the reason why this theorem came to be called the pons asinorum is that it was thought to be difficult to persuade asses to cross a bridge. One assumes that we are dealing with fairly narrow bridges made of timber, as a result of which the asses would be nervous of falling.
There is, however, another asses' bridge, much less known. During the last stages of initiation into the Eleusinian mysteries in ancient Greece, one of the tasks set initiates was for each initiate to individually cross the bridge leading from the town into the sacred enclave. On the parapet of the bridge, the priests were perched, wearing masks in the form of asses' heads. The priests then publicly hurled insults at the crossing initiate, accusing him or her of his or her (women were welcome to attend the mysteries) vanities and faults, e.g. by calling the initiate arrogant, pompous, pretentious, greedy or whatever was appropriate in a particular case. The idea behind it was to publicly force the initiate to see his or her faults and to confront them in order to grow beyond these faults. This ordeal was referred to as the pons asinorum, and by such accounts as are available (it was sacrilege to divulge what occurred during the mysteries, resulting in very little direct evidence as to what occurred inside the sacred enclave), it was an extremely humbling as well as humiliating experience.
The pons asinorum is therefore also the personal ordeals all of us have to face occasionally, from which we (ought to) learn and grow. | 
