If you don't see the virtue of friendship and harmony, you may learn it by observing the effects of quarrels and feuds. Was any family ever so well established, any State so firmly settled, as to be beyond the reach of utter destruction from animosities and factions?
 Marcus Tullius Cicero, On Friendship (44 BC). copy citation

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Author Marcus Tullius Cicero
Source On Friendship
Topic friendship destruction
Date 44 BC
Language English
Reference
Note Translated by E. S. Shuckburgh
Weblink http://www.gutenberg.org/files/2808/2808-h/2808-h.htm

Context

“While they take the sting out of death, they add a glory to the life of the survivors. Nay, if you eliminate from nature the tie of affection, there will be an end of house and city, nor will so much as the cultivation of the soil be left. If you don't see the virtue of friendship and harmony, you may learn it by observing the effects of quarrels and feuds. Was any family ever so well established, any State so firmly settled, as to be beyond the reach of utter destruction from animosities and factions? This may teach you the immense advantage of friendship.
They say that a certain philosopher of Agrigentum, in a Greek poem, pronounced with the authority of an oracle the doctrine that whatever in nature and the universe was unchangeable was so in virtue of the binding force of friendship; whatever was changeable was so by the solvent power of discord.” source