Merlin is an avid reader.
He reads absolutely anything he can get his hands on. Histories, myths, epic poems—even Gaius's physician books, although he can't understand half of what's in those ones. Geoffrey, the bookkeeper, always mutters that Merlin is going to ruin whatever book he's borrowing this time, but Arthur has seen children that weren't taken care of as well as Merlin cares for those books.
Merlin's duties keep him busy during the day, between assisting Gaius and helping Arthur, so he usually reads at night as they're lying in bed. He props himself up on all of the pillows, not even leaving one for Arthur, which means Arthur has to use Merlin's lap as a pillow instead. He complains but really, he doesn't mind. Not when Merlin is carding his fingers through his hair, nails scratching gently at the nape of his neck, his body warm and solid beneath Arthur. When Merlin finds something he thinks Arthur will like, he reads it out loud. Arthur has learned more about the history of Albion from Merlin's bedtime readings than from all of his lessons as a child. Merlin's voice is low and soothing, the words tumbling off of his tongue like water going over a waterfall, cascading down before sliding deep into the pool below.
Oftentimes Arthur falls asleep like that, with Merlin's fingers in his hair and Merlin reading silently. Once a while he wakes up as Merlin's blowing out the candle and setting the book aside, slinking down the bed to curl up with Arthur, his eyelids drooping from reading so late. And every once in a while, as Arthur is drifting off to sleep, he can hear Merlin hum a song. He can never quite identify what song it is, but it's probably something Hunith sang to him as a baby. Merlin hums it softly, trailing off here and there, and Arthur lets the sound sink into his skin, into his memory, so that he will never forget it.
Sometimes, Arthur thinks these moments might be his favorite of all.