K.R.
"We have refused to, threatened, and even swatted, and he will not give in."
My only comment for you is that a child who is met with angry parents -- who hit him -- can not possibly relax enough to go to sleep. The issue sounds like he is unable to self-soothe, and if you respond with anger, his stress level will go up and he REALLY won't be able to sleep.
As hard as it is, you must be entirely calm and relaxed when you deal with him when he won't fall asleep.
Meanwhile, you should read some books about sleeping (Healthy Sleep Habits, Happy Child, by Weissbluth is a particularly good one) and learn more about helping him self-soothe. Good luck. I know it's very frustrating.