'Seventy' in the Bible

Ahab had seventy sons living in Samaria. So Jehu wrote letters and sent them to Samaria to the leading officials of Jezreel and to the guardians of Ahab's dynasty. This is what the letters said,

He wrote them a second letter, saying, "If you are really on my side and are willing to obey me, then take the heads of your master's sons and come to me in Jezreel at this time tomorrow." Now the king had seventy sons, and the prominent men of the city were raising them.

When they received the letter, they seized the king's sons and executed all seventy of them. They put their heads in baskets and sent them to him in Jezreel.