'Seventy' in the Bible

Now Ahab had seventy sons in Samaria. And Jehu wrote letters, and sent to Samaria, unto the rulers of Jezreel, even the elders, and unto them that brought up the sons of Ahab, saying,

Then he wrote a letter the second time to them, saying, If ye be on my side, and if ye will hearken unto my voice, take ye the heads of the men your master's sons, and come to me to Jezreel by to-morrow this time. Now the king's sons, being seventy persons, were with the great men of the city, who brought them up.

And it came to pass, when the letter came to them, that they took the king's sons, and slew them, even seventy persons, and put their heads in baskets, and sent them unto him to Jezreel.