"These are their stories..."

Law & Order holds a unique place in television history. It's one of the longest-running primetime dramas ever — only Gunsmoke and Bonanza, both of which hit the 20-year mark, hung around longer. It has also spawned a legion of spinoffs, some successful (Law & Order: Special Victims Unit, Law & Order: Criminal Intent), others not so much (Law & Order: Trial By Jury, the just-cancelled Conviction).

But perhaps L&O's greatest feat has been its ability to maintain its popularity despite near-annual cast changes. It's been a rare season when the venerable detectives-and-district attorneys series hasn't swapped out at least one of its six continuing roles:

• The Senior Cop: Originally George Dzundza as Max Greevey, followed briefly by Paul Sorvino as Phil Cerretta, then a lengthy stint by the late Jerry Orbach as the beloved Lennie Briscoe, and for the past two years Dennis Farina as Joe Fontana.
  
  
• The Junior Cop: Chris Noth's Mike Logan (who currently is part of the L&O:CI team), then Benjamin Bratt as Reynaldo Curtis, and most recently Jesse L. Martin as Ed Green (plus a six-episode spotlight for The Sopranos' Michael Imperioli while Martin was away filming Rent).
  
  
• The Boss Cop: Dann Florek's Don Cragen (now the Boss Cop on L&O:SVU) was replaced more than a dozen seasons ago by S. Epatha Merkerson's tough Anita Van Buren.
  
  
• The Lead Prosecutor: One of the series' more stable roles, first held for five seasons by Michael Moriarty as Ben Stone (the same name, incidentally, as Michael J. Fox's character in Doc Hollywood), and ever since by Sam Waterston as the wily Jack McCoy.
  
  
• The Assistant Prosecutor: A veritable revolving door, this role has experienced the highest degree of turnover since Richard Brooks (the only male actor to hold the spot thus far) was dismissed along with Florek in a gender-equity move by NBC after the show's third season. In the wake of Brooks's Paul Robinette came Claire Kincaid (Jill Hennessey, now the star of Crossing Jordan), Jamie Ross (Carey Lowell, aka Mrs. Richard Gere), Abbie Carmichael (Angie Harmon, most recently in the short-lived Inconceivable), Serena Southerlyn (Elisabeth Rohm, whose character came out as a lesbian in her signoff episode), and the ill-fated Alexandra Borgia (Annie Parisse), who was killed off in the last episode of the season just concluded.
  
  
• The District Attorney: Steven Hill's crusty Adam Schiff (does anyone else recall Hill as the original lead on Mission: Impossible, preceding Peter Graves?) gave way after a lengthy tenure to Dianne Wiest's pragmatic Nora Lewin, then to the former U.S. Senator from Tennessee, Fred Dalton Thompson, typecast as gruff conservative Arthur Branch.

Well, L&O fans, the wheels are spinning again. Dennis Farina won't be returning to the show next season, joining the aforementioned Annie Parisse in the unemployment line (albeit voluntarily in Farina's case — Parisse, whose character never seemed to develop a personality, was shown the door). In a first-ever move for the series, Jesse Martin's Ed Green will be promoted to Senior Cop, filling Farina's vacancy, with actress Milena Govich porting over from the late, unlamented Conviction as a new, as-yet-unnamed Junior Cop — the first female in that role in L&O history.

On L&O, the more things change, the more they stay the same.