A choice of a horse as the shape of Amara's fury seems odd at first—horses aren't generally wind-associated creatures. But with the series' recurring Chess Motif, it's obvious: Amara regularly overcomes powerful lords by outmanoeuvring them, as well as repeatedly penetrating enemy territory through guile, skill and non-linear thinking. In other words, she's a knight.
A lot of things about that reveal become Fridge Brilliance on a reread: For instance, the First Lord's line towards the end of the first book: "A princely gift. Are you sure it is yours to give?" He said that to Fade, regarding a sword taken from the Princeps' Memorium. So he's talking to Septimus's singulare about giving one of the singulares' swords to the prince. Thereby making it very clear to Araris that he knows exactly what's going on. No wonder he agreed to go to the capital.
At first, it appears as though Gaius Sextus didn't care for his "wife" because he was so wrapped up in politics and ruling his kingdom. Then it becomes apparent that Gaius Sextus could summon Alera anytime he wished—a superhumanly beautiful and impossibly intelligent and wise and friendly female entity—one with whom he has an equal partnership. Gaius Sextus was, in a way, married to Alera. It's not clear if there was anything sexual going on between them, but Alera would provide a partner, friend, and companion far more fulfilling and far more equal to someone like Gaius than his politically-married wife ever could.
Minor one: When Tavi's using fire- or metalcrafting, the sparks and flames are red and blue. The colors of House Gaius.
Jim Butcher wrote the Codex Alera by combining what he thought were two bad ideas: The Lost Roman Legion and Pokémon. Now consider that one of the most powerful and dangerous furies in the series is named Garados. There's also Isana, a Mama Bear among Mama Bears, using a Fury she calls Rill (as in "Ma-rill").
Cursor's Fury is full of these. (1) Magnus (or Max) explains to Tavi early on that anyone competent in the new Aleran legion will be a spy. At the very end of the book, we learn why Alera's version of Sergeant Rock came out of retirement for the job. (2) At the end of that sequence, Butcher reminds us that Gaius Sextus knows who Sergeant Rock really is, that he therefore couldn't come out of retirement without Gaius's approval, and that Gaius set up the whole Aleran legion for Tavi's benefit. In other words, Gaius turned Fidelias back to the cause by showing him Tavi in action. (3) Lastly, Gaius reveals that he knows full well what "Tavi" is short for.
The symbolism behind Fade/ Araris' self mutilation of himself by branding himself with the Legion's mark of cowardice. While he did it to disguise his identity from those around him, he also did it because he felt he exhibited cowardice by abandoning Septimus in the field, even though Septimus ordered him to.
Since he's almost always referred to as a slave, rather than by his profession, it's easy to miss that Fade, secretly one of the finest metalcrafters alive, works as a blacksmith.
The choice of pictures for the cover of this book. Each cover represents a high-level use of each kind of Aleran furycraft. Furies of Calderon - Wind ( the windmanes), Academ's Fury - Earth ( the arms of Earth used to restrain Tavi), Cursor's Fury - Water ( the two water lions sent by Max and Crassus), Captain's Fury - Fire ( the firehounds guarding the Gray Tower), Princeps' Fury - Wood ( the figurehead of the Slive bending over to pick Tavi up), and First Lord's Fury - Metal. The British versions have symbols for what appears to be fire(Garm's Fearcrafting), Water(Max's impersonation of Gaius, Air(The air-lenses used to win the battle with the Canim), Earth(the Legionaires' defenses, on both sides), Wood, and Metal. The German covers are more direct.
Tavi's Sword Sparks are blue and red, his family's colors and those of Alera itself.
One would think that "Tavi" is a very weird sounding name. Or at least, that it doesn't fit in a world of Awesome McCoolnames. And it appeared as if Butcher was shamelessly rubbing that name in our faces for 3 books. Well, that was until the fourth book, where it was revealed that Tavi stood for Octavian... as in Sextus-Septimus-Octavus.
Ever wonder why the Vord Queens are so unconventionally intelligent and such brilliant strategists and tacticians, and how they develop such potent furycrafting? Tavi bled on the Vord Queen's mound in Furies of Calderon. They picked up Tavi's furycrafting talents and intelligence directly from him. It's no coincidence that the primary Vord Queen picks up furycrafting at the same time as her "parents."
From Books 2 through 6, the titles all follow a specific pattern. All of them refer to Tavi at various stages of his Hero's Journey ... except the first. Furies of Calderon doesn't seem to fit ... until you remember one detail from the later books. What's Max's nickname for Tavi? Calderon. The working title was Shepherd Boy's Fury.
In Book 1, Frederick uses a spade as a weapon. This may seem a humorous reference to his farmboy nature and nothing more... Until one realizes that the Roman word for spade, 'Spatha' is also the word for the Roman Broadsword. (And indeed there's some evidence early Spatha swords saw double use for digging and cutting of both roots and limbs).
The way the Lords make lots of small fires rather than just big ones is an example of Tavi's preference for efficiency over the traditional Aleran brute force.
How did Tavi manage to anticipate exactly which street The Black Cat was going to rob, not once but twice? Because he's telepathically bonded to her
Tavi's alias during his stint as subtribune and later captain of the First Aleran is Rufus Scipio. This is possibly a reference to Scipio Africanus, another badass general.
Tavi is a farmboy and rises to be First Lord and that Title is reserved for the strongest man is Alera. In Pokemon, a basis for the series, the player starts as a kid from the smallest town and becomes champion, the strongest in the game. As a further nod to the games Tavi frequently encounters the Vord and defeats them. The Vord Queen kills the First Lord and becomes the final opponent Tavi must face, as a reference to the rival being the champion at the end of the first set of games.
The Vord Queen isn't just that...the Vord Queen is also an immensely powerful being with psychic powers, artificially engineered to be the best and strongest. She's Mewtwo.
And one more for the road: The colors of Aquitaine, who have some shadowy operatives and continually oppose the main character but are rarely ever main antagonists, are red and black—the same as Team Rocket.
Why do the archers not wear armor? Most series say it allows them to move and bend better. But in Codex Alera the archers are woodcrafters. Metal cancels their abilities rendering them useless. Even a few metal bands can cancel a woodcrafters skills, imagine what a full set of armor would do.
On reflection, Tavi and his close circle of friends all reflect different outsiders from Aleran society. In a culture that prizes furycrafting, Tavi has none and Ehren very little. Kitai is a nonhuman in a humanocentric, xenophobid empire (and she's also an outsider among her own people, for that matter, not having a clan). Even Max, handsome, likable son of a powerful nobleman, is a bastard and suffers both a degree of social stigma and, more directly, a homicidal stepmother. Of course, that's just where they start, but still...
At the start of "Cursor's Fury", Gaius tricks Kalarus into acting too early with a faked letter claiming he's going to adopt Lord Aquataine as his heir. His later actual adoption of Aquataine makes it almost certain that it was his real plan as well if Tavi hadn't developed crafting. And if you think about it, Attis may be a bastard (in the metaphorical sense) but he's smart, charismatic, relatively young, and a really powerful crafter and he's got the Realm's best interests at heart, though his methods are often questionable at best. Out of all the High Lords, he's honestly probably the best choice for a successor until Tavi develops into someone better.
Invidia has more in common with the Vord Queens than she probably realizes—in Academ's Fury, just before she dies, the Vord Queen is completely taken aback by the very idea that the Alerans would knowingly come out to die for the chance to kill her. Later in the series, after Invidia comes into the Prime Queen's service, she defends her actions by saying she had no choice, because she would've died if she hadn't. Like that first Queen, she simply could not wrap her head around the idea of sacrificing herself for a higher purpose.
The most powerful forces in the Calderon Valley are the Earth fury Garados, and his wife, the Wind fury Thana. By the end of the series, the people in charge of the Valley are...the Earthcrafter Bernard, and his wife, the Windcrafter Amara.
Consider the way Fade acts throughout Furies of Calderon. He's always grabbing Tavi, knocking or pulling him down, and gibbering in fear. Once Fade's true identity is revealed, it becomes clear that he was protecting him, as each time he did something like this it directly took Tavi out of immediate danger.
When Gauis Sextus collapses in Academ's Fury Sir Miles says the only people he trusts died twenty years ago, most likely referring to Septimus, Araris and the others. Who does Tavi fetch to help them? Fade, who is Miles' brother Araris, presumed dead for twenty years.
Not sure if this qualifies, but there isn't a Fridge Awesome section, either. At the end of the series, Tavi seems to have made crafting available to everybody, regardless of race. Canim. Earthcrafters. The Vord are screwed. Imagine how monstrous those weapons would be. On top of that, crafting becomes Merit based rather than bloodline based. So the more awesome you are, the better you are at all forms of crafting. Canim live longer than humans. Say hello High Lord VARG, now one of the best crafters in the world.
The Vord Queen's offer to protect surrendering Alerans with the "full might of the Vord" seems a little odd when you consider that, once the Vord overrun the planet, there won't be anything left to threaten their lives. That's when you remember that the prime Queen is considered 'defective' by other Vord, that every new Queen she spawns has a genetic imperative to kill her, and that one such Queen is in complete control of Canea and all of its resources. The Alerans would need protecting eventually, because one day the Canea Queen is going to cross the sea and send her Vord against the prime Queen.
Back in Academ's Fury, while Tavi's out trying to catch the furyless cat burglar, he bumps into Maximus. He tries to excuse himself by insinuating he's out to meet a girl, and Max laughs it off, saying he couldn't possibly be meeting a woman in that state. Gets a lot funnier when you know the cat burglar is Kitai, huh?
The Slave Collars are Pokeball analogs. You can only be released by the one who collared you, and if you're already collared, a second collar will automatically fail.
Masha's father turns out to have been the younger Kalarus Brencis. Every time High Lord Kalare threatened her to keep Rook in line, he was threatening his own granddaughter.
The Marat clans fight each other all the time, frequently enough that they have a system to stop the fighting quickly and let the leaders talk it out. Marat children are by no means guaranteed to stay with the clan they were born into; they go with whatever their totem is. Family members are likely to meet each other in combat all the time.
Tavi makes crafting available to ALL... Alerans were only formidable for their discipline, and Furies. Alerans are smaller and weaker than literally every other sentient race, Marat are faster, stronger, hardier, and the Canim are even moreso. Tavi has made it so that Alerans will be totally obsolete after a few generations.