WALTHAM -- You might remember Kevin Garnett feuding with Zaza Pachulia during the 2008 playoffs. Al Horford certainly does. As an Atlanta Hawks rookie that season, he helped the Hawks challenge the Celtics in a surprisingly competitive seven-game series. Horford recalls something you don't, though: the way it felt to play underneath all of Boston's championship banners.

"I'm not gonna lie," Horford said Monday at media day. "The first time I played in the Garden my rookie year I couldn't stop looking at the banners up top. Maybe some guys feel differently, but I couldn't stop looking at them. It's powerful, it leaves an impression on you."

When it came time to pick a team in free agency this summer, Horford remembered that feeling. By itself it wouldn't have been enough to sway him, but the rest of the Celtics situation sang to him too. He accomplished so much with the Hawks, led the team to some of the best years in franchise history. Still, Horford looked over at Boston's roster and noticed the youth, athleticism and promise. Even when he knocked the Celtics out of the playoffs, the strength of their future struck him.

"We all know the situation of the flexibility and all the future draft picks and all that stuff," Horford said, wearing a Celtics jersey on the practice court for the first time. "That was there. But for me, just the guys that we have here, the group that's here is what I felt good about with Coach (Brad) Stevens, playing under his system."

"I was very impressed with how hard the guys played and how good the team could be under Coach Stevens and just what I saw from the group," Horford added. "It just really intrigued me and when the free agency process came around at the beginning, I would say I was very comfortable with Atlanta, but as the time kept going on and I met with the Celtics it just became real to me. Looking at my career at this point, I'm going into my 10th year and want to be able to be a part of something special and win a championship, and with the type of guys that we have here, we have that possibility and that's something I wanted to be a part of."

The c-word? Don't get ahead of yourself. The Celtics aren't ready to challenge yet.

"We have a long way to go to be considering talking about any of that stuff," Stevens said. "And to be quite frank as I told our team real briefly before we walked out here, there was not a lot of room between finishing 10th and second last year in the East. Ultimately we want to be the best, we want to be among those considered the best. There's a lot of hard work ahead of us, and it's day by day. I don't feel any more pressure from what ultimately happens. I'm making sure that practice tomorrow is structured right.

"My expectations never change. It's all about getting tomorrow and making sure we're as good as we can be. It's a very simple, boring process but it's the way that I go about it. And I think that the results take care of themselves."

With Horford on board, the Celtics believe they should continue their upward trajectory. Though they haven't even held their first official practice, the Horford reviews are starting to grow predictable and boring. One by one, members of the organization reword the same compliment. It usually goes something like this: Horford should lift the Celtics in just about every category, across the board, on and off the court.

"What is he not going to help us with?" said new teammate Jonas Jerebko, essentially summarizing everybody's thoughts.

Even with Horford, though, the Celtics need to grow. Last season ended with Isaiah Thomas weeping in the locker room. As he explains it, he had given everything he had to a basketball team for the first time of his life. He had wanted so badly to drag the Celtics out of the first round, but they failed to advance for the second straight season. He cried for a long time that night and the feeling stuck with him.

"All offseason, that's all I thought about," Thomas said.

"Losing that series left a bad taste in all of our mouths," the All-Star guard continued. "We want to get past that first round. I do, I know that. I want to go further. We have a good team, and people to make that happen. Last season hurt me especially because that's the first time I can say I gave everything I had - I had no more left in me, and that's why I hurt so much. Having everybody back for another year, we're looking for bigger and better things. What that may be we don't know, but hopefully we can jell faster than we did last year with the additions we have on this team."

The Celtics won 48 games last season. One Las Vegas sports book set the team's over-under at 51.5 wins in the coming campaign.

"The guys had a really good year last year here," Horford said. "We have some great leaders here already, and I just want to be able to come in and help our team grow, just get acclimated as fast as I can and help us be a better team. That's basically what I'm here to do. I want us to grow as a team and be better. I took a chance on coming here because I believe in the type of guys we have here in the organization, and the potential there is."