Herodotus, Histories 1. 31. 1 (trans. Godley) (Greek historian C5th B.C.) :
"Kleobis and Biton were of Argive stock . . . and this story is told about them : there was a festival of Hera in Argos, and their mother absolutely had to be conveyed to the temple by a team of oxen. But their oxen had not come back from the fields in time, so the youths took the yoke upon their own shoulders under constraint of time. They drew the wagon, with their mother riding atop it, traveling five miles until they arrived at the temple. When they had done this and had been seen by the entire gathering, their lives came to an excellent end, and in their case the god made clear that for human beings it is a better thing to die than to live. The Argive men stood around the youths and congratulated them on their strength; the Argive women congratulated their mother for having borne such children. She was overjoyed at the feat and at the praise, so she stood before the image and prayed that the goddess might grant the best thing for man to her children Kleobis and Biton, who had given great honor to the goddess. After this prayer they sacrificed and feasted. The youths then lay down in the temple and went to sleep and never rose again; death held them there. The Argives made and dedicated at Delphoi statues of them as being the best of men."
"Kleobis and Biton were of Argive stock . . . and this story is told about them : there was a festival of Hera in Argos, and their mother absolutely had to be conveyed to the temple by a team of oxen. But their oxen had not come back from the fields in time, so the youths took the yoke upon their own shoulders under constraint of time. They drew the wagon, with their mother riding atop it, traveling five miles until they arrived at the temple. When they had done this and had been seen by the entire gathering, their lives came to an excellent end, and in their case the god made clear that for human beings it is a better thing to die than to live. The Argive men stood around the youths and congratulated them on their strength; the Argive women congratulated their mother for having borne such children. She was overjoyed at the feat and at the praise, so she stood before the image and prayed that the goddess might grant the best thing for man to her children Kleobis and Biton, who had given great honor to the goddess. After this prayer they sacrificed and feasted. The youths then lay down in the temple and went to sleep and never rose again; death held them there. The Argives made and dedicated at Delphoi statues of them as being the best of men."
