"At the start of the year...."
It's spring, and the siege of Rabbah is underway.
Rabbah is the capital city of Ammon, and the importance of this siege can be judged from the fact that the Ark has accompanied the army of Israel. (2 Sam 11:11).
But where is the king?
He has stayed in Jerusalem, leaving the attack to Joab. (1).
Although not mentioned here in Chronicles, we know that these circumstances led to David's grievous sin :
He saw Bathsheba from his rooftop, wanted this beautiful woman for himself, took her, and caused the death of her husband Uriah to cover up his crime when she fell pregnant.
Meanwhile, at Rabbah Joab was having great success, and thinking his sin had been entirely concealed, David came to Rabbah to complete the conquest, taking "a vast amount of spoil from the city".
The crown of Malcam (or Molech) was placed (seemingly momentarily according to the research notes, because of its weight) on David's head, signifying total victory over both the Ammonites and their god. (2).
As for the city's inhabitants, they were "put to work at sawing stones and working with sharp iron instruments ". (3).
Some earlier scholars have described David's actions as cruel and barbaric, having misunderstood the original text.
However, we now have more accurate modern translations that make it clear these people were simply put to use as labourers. (See research notes).
This is entirely in accordance with what we know of David's character and temperament.