Earlier this month, Ravens director of player personnel Eric DeCosta described the theme of this weekend's NFL draft as a "depth draft for the Ravens at virtually every position."

And to round out a roster that team officials feel can be molded into another Super Bowl contender, the Ravens spent Saturday's final day of the draft diving deep into the collegiate talent pool.

The final four rounds of the Ravens' 2012 draft were highlighted by the selection of a trio of small-school prospects who filled secondary needs. In the fourth round, the Ravens drafted Delaware interior lineman Gino Gradkowski and South Carolina State free safety Christian Thompson. At the end of the fifth, they took Cal Poly cornerback and kick returner Asa Jackson.

Though he pointed out that Gradkowski and Thompson experienced major college football before transferring to their current schools, DeCosta said the Ravens' scouting department — regarded as one of the best in the NFL — enjoys the challenge of trying to find the next Joe Flacco or Lardarius Webb.

"We take pride in really looking at these small-school guys and being able to compare these guys to the big-school guys," he said. "I think scouting has become so good around the league that there are some good players at some of these small schools, and I think there is an opportunity there for us to maybe take advantage of our scouts and find some of those guys."

In the final two rounds, the Ravens added additional depth at wide receiver with Miami's Tommy Streeter and on the defensive line with Georgia's DeAngelo Tyson.

Before this weekend, the Ravens had never selected a player from Iowa State, Temple, South Carolina State, or Cal Poly. And Flacco was the only player they had drafted from Delaware.

But after drafting Alabama outside linebacker Courtney Upshaw with their first pick in Friday's second round, Ravens general manager Ozzie Newsome ventured into uncharted territory by picking Iowa State guard Kelechi Osemele and Temple running back Bernard Pierce. A day later, the Ravens mined the Football Championship Subdivision (formerly Division 1-AA) ranks for lesser-known prospects.

The Ravens have hit on two FCS prospects in recent years — drafting Flacco in the first round in 2008 and Webb, a Nicholls State defensive back, in the third round in 2009.

Newsome said the organization has shifted its focus in recent years to scour the lower levels for talent, in part because the information available to NFL teams continues to increase.

"We go into the small schools and do the same amount of work as the big schools," Newsome said as the seventh round wound down. "Our scouts, when they go into the Delaware or the Cal Poly or the South Carolina State, it's just like when they go into Ohio State, Maryland or Alabama."

And when players they coveted at the top of their board were selected by other teams throughout the weekend, DeCosta said the Ravens "had to get creative quickly on the fly."

"Things don't always happen the way you want them to," DeCosta said. "Some drafts, every player that you want kind of comes to you. And other drafts — this year comes to mind, 2010 was very similar to this year — sometimes you just get wiped out and you have four players and all the sudden, boom, they're done, and you have to get creative."

The Ravens said before the draft that they wanted to add offensive linemen, a pass rusher, and a wide receiver. They also wanted to add more depth in their secondary and at running back. A dangerous return man was also on their lengthy shopping list.

Coach John Harbaugh admitted the cap-strapped Ravens — who live by the draft mantra of "take the best player available" — felt they had to fill holes on their roster through the draft.

"You always try to draft the best player out there and try to make your team as strong as you can, but there is also the element of need," said Harbaugh, the only coach to take his team to the past four NFL postseasons. "We do have some opportunity in there for these guys to play."

Gradkowski, the younger brother of Cincinnati Bengals quarterback Bruce Gradkowski, transferred to Delaware from West Virginia and became one of the top linemen in the Colonial Athletic Association. The 6-foot-3, 300-pound Pittsburgh native played both center and guard in his senior season. He said he's eager to pick the brain of veteran center Matt Birk.

Even with the return of Birk, who signed a three-year contract to remain in Baltimore, the Ravens wanted to draft and develop a long-term replacement at the center position. They passed on more notable center prospects from major programs — among them were Georgia's Ben Jones, Baylor's Philip Blake and Michigan's David Molk — to select Gradkowski.

"He's a tough kid," Harbaugh said. "He's a quick-footed, really athletic center. ... We are going to start him off at guard probably and move him in at center as we go and see how it goes."