The foundation has been put in place. Castillo works his locker room, going from player to player and talking to them with enthusiasm and gusto and confidence about what is ahead for 2012. He is a man of preparation and energy, and Castillo has an idea of what he wants from each and every one of his defensive players.

What changes can we expect from a defense that was inconsistent through much of 12 games last season before turning in a lights-out performance in the final four weeks? It was almost as if the switch had been flipped for Castillo and his defense in the last month. All of a sudden his blitzes got home. Just like that, the defense found its rhythm and slowed running games and covered down the field and made plays in the red zone.

It was with those four games fresh in their minds did Castillo and the defense head into the offseason with so much good feeling. Now, after adding middle linebacker DeMeco Ryans, retaining tackle Derek Landri and drafting tackle Fletcher Cox, linebacker Mychal Kendricks, defensive end Vinny Curry and cornerback Brandon Boykin, the optimism is positively bubbling over.

There is a ton of work to be done before anyone pronounces the defense as complete. The Eagles must get their rotation in order along the front four, but that is something for veteran coach Jim Washburn to handle -- and to enjoy in the process. Rarely in his career has he had so much talent with which to work. He wants to wear down offensive lines in waves and beat them with speed and aggressiveness and power. He has all of those talents here.

At linebacker, Ryan must step right into the position and take control of the defense and be the physical, playmaking middle linebacker the Eagles have lacked since the days of Jeremiah Trotter in the mid-2000s. Stewart Bradley offered glimpses and Jamar Chaney had spurts, but the Eagles crave consistency at that position. In fact, the entire linebacker group could use some stability. A source of movement for more than a decade, the linebackers have enough pieces here to hope for a few to emerge and to stay here for the long haul.

From a positional standpoint, there is a lot to finalize at linebacker. Is Kendricks, as suspected, first on the depth chart at SAM linebacker? We won't know for sure until the June full-team mini-camp, but the second-round draft pick is going to get every chance to win that job. Is the weak-side job a battle between incumbent Brian Rolle and Casey Matthews, who is bigger and stronger after an offseason of hard work in the weight room? Where does Chaney fit into the picture?  What about veterans like Moise Fokou and Akeem Jordan, both of whom had their moments in the defense last season?

The back four has similar questions now that Asante Samuel has been traded and Dominique Rodgers-Cromartie joins Nnamdi Asomugha in the starting lineup. They are expected to use their length and strength in more press coverage at the line of scrimmage. Castillo will mix things up, but the thought here is that the days of "off" coverage on such a consistent basis are pretty much finished.

Who assumes the nickel cornerback position? Does Joselio Hanson beat off the challenge from Boykin? Does Curtis Marsh step up? Are any of the other young cornerbacks prepared to make a move?

The Eagles did not add a safety in the draft, although they feel good about their post-draft work there, so it is likely that Nate Allen will be paired with Kurt Coleman or Jaiquawn Jarrett in the deep part of the defense, and of course the Eagles need to be better at safety than they were last season.

Above all of that, what changes is Castillo going to implement in 2012? He moved end Jason Babin all around the line of scrimmage late in year once he became comfortable with what Babin could handle. Matthews earned a starting role in the nickel defense and all of a sudden flew to the football and made plays. He experimented with Asomugha all season, and not until Samuel went out with a hamstring injury and Rodgers-Cromartie became the starter did the cornerbacks really shine.

There are big plans with this defense, no question. The middle of the defense has been fortified. The Eagles should be a more physical team. They want to be aggressive. They want to live on sacks, and takeaways and stops in the red zone.

These last few seasons have been tough on the defense, what with the death of former coordinator Jim Johnson, the departure of safety Brian Dawkins and the very quick aging of a roster coupled with some draft-day injuries and misses.

It appears, though, that the defense has all of the pieces in place for a revival. The Eagles are set to take the momentum they got rolling last December and keep that going this season. A lot of questions have to be answered first, though, but there is plenty of reason to feel optimistic about Castillo and his defense looking ahead.

NEWS, NOTES AND A LITTLE BIT OF THIS AND THAT

• The Achilles tendon injury suffered by Baltimore linebacker Terrell Suggs means, in all likelihood, that he will not play in the Week 2 game at Lincoln Financial Field. Suggs' injury is a huge blow to a Ravens defense that has been among the NFL's best for a long, long time.  The Ravens had some ups and downs last year, but always have a feared defense. Losing Suggs means that rookie Courtney Upshaw has to step in and learn on the fly.
• Will the Eagles see rookie quarterback Brandon Weeden when the season opens in Cleveland? The idea of seeing both Weeden and running back Trent Richardson, both of whom the Browns drafted in the first round last week, is exciting.
• The Eagles hold their Rookie Camp starting next Friday when the 2012 Rookie Class starts to arrive at the NovaCare Complex. The team will have two practices per day Saturday and Sunday and then another one on Monday. Head coach Andy Reid meets the media once, after Monday's practice.
• Suddenly, nobody is talking about adding a running back or a safety to this roster. The Eagles want to look at their young players in these spring camps and see how they retain information, how they run, how athletic they are and how they accept coaching. There is still a lot of veteran talent on the streets. Amazing that free agency came to such a crashing halt so quickly.