The center back position is a thin one for the Philadelphia Union. It is also, one full of unproven players. Currently, there are three center backs on the roster not counting Maurice Edu (who is an emergency option), and between them they have 21 games of MLS experience (all going to Richie Marquez). The Union's center back depth lines up like this:

Richie Marquez (Age 23) - Marquez is an undisputed starter for the Union at center back this year. It was a tough choice between him and Conceição for the top spot, but I had to pick the player with actual MLS experience. Marquez has shown flashes of being able to be an above average MLS defender, and this year may be the year that Marquez does that consistently. With a steady partner beside him that actually holds defensive positioning (I'm looking at you Edu), Marquez should be much more comfortable in making Andre Blake's life easier in goal. Anderson Conceição (Age 26, International player) - I can't say that I know much about the Brazilian Série B where Conceição gained most of his experience, but being on a back line of América Mineiro and helping them achieve promotion to Série A this past season will bring experience and steel to the Union. I struggled with ranking Conceição vs, Marquez because even though they are very different players, I think Conceição has better positioning and can be an asset with the ball at his feet. Because of that, Conceição brings a different skill set to the Union back line than they are used to having (Earnie Stewart finding players to fit the style that he wants to play). Once he gels and gets up to speed in MLS, Conceição could be the Union's most important signing. Joshua Yaro (Age 21, International player, Generation adidas) - Hailing from an impressive Georgetown back line that led the Hoyas to a 16-2-3 record and a NCAA Sweet 16 performance Yaro comes with some of your prototypical prospect hype. He's a little undersized for a center back at 5'11", but makes up for that with impressive speed, ball skills and positioning. It will take some time for Yaro to get acclimated to the MLS, but he has the skills to form a long term partnership with Marquez and/or Conceição in the future. Yaro will mainly get experience in Open Cup games and as a rotational piece (barring that there isn't an injury crisis), and that should be about the right spot for the rookie. Maurice Edu (Age 29, Emergency center back) - Say it with me now, "Please don't let Maurice Edu play center back for the Union this year. Please don't let Maurice Edu play center back for the Union this year." Ok now that we've gotten that out of our systems, let's face the fact that if Maurice Edu is playing center back for the Union this year a lot has went wrong. Jim Curtain has stated, "He has done whatever we asked him but now we see him as the No. 6," Even with this, Edu is a backup at center back, if only because of his experience there. While he is competent in the back, Edu's attacking mentality and positioning won't get to the point where he can become a reliable center back. While the Union should be ok if Edu plays a few games in central defense, they will be in trouble if he has to be a consistent starter. Ken Tribbett (Age 23, Bethlehem Steel) - Tribbett has impressed since coming into the Union camp. The ex-Harrisburg City Islanders center back signed with Bethlehem Steel FC during the offseason but has been praised by Curtin for his abilities. It would not be surprising to see Tribbett get minutes during the Open Cup or in the event of injury/suspension. Michael "Mickey" Daly (Age 28, Bethlehem Steel FC)- Daly is a USL veteran who will be tasked with holding the Bethlehem Steel FC line. Daly has played with the Wilmington Hammerheads and Sacramento Republic FC while being a solid contributor to both teams. He may never contribute to the Union's first team, but his leadership qualities will be huge for what will probably be a young team in Bethlehem.