The 12-Mile Circle is an approximately circular arc which forms most of the boundary between the Commonwealth of Pennsylvania and the State of Delaware in the United States. It is not actually a circle, but rather a combination of different circular arcs that have been imperceptibly feathered together.

It is nominally a circle with a supposed—yet in fact only approximate and variable—12-mile radius, centered in the town of New Castle, Delaware. In 1750, the center of the circle was fixed at the cupola of the courthouse in New Castle (however, subsequent changes have also been based on a different center point, several thousand feet to the northwest of the courthouse). The 12-Mile Circle continues into the Delaware River. A small portion of the circle, known as the "Arc Line," also forms part of the Mason-Dixon line, separating Delaware and Maryland. And two other small portions, although not actually demarcated until 1934, form parts of the boundary between the states of Delaware and New Jersey. Although the 12-Mile Circle is often claimed to be the only territorial boundary in the United States that is a true arc (excepting those following arcs of latitude and longitude), the Mexican boundary with Texas includes several arcs, and many cities in the South (such as Plains, Georgia) also have circular boundaries.

Thomas William "Tom" Selleck (born January 29, 1945) is an American actor and film producer. He is best known for his starring role as the private investigator Thomas Magnum in the television series Magnum, P.I. (1980s), which was based in Hawaii. He also plays Police Chief Jesse Stone in a series of made-for-TV movies based on the Robert B. Parker novels. Since 2010 he has appeared as the NYPD Police Commissioner Frank Reagan in the drama Blue Bloods on CBS-TV.

Selleck has acted in many TV roles, including Dr. Richard Burke on Friends and A.J. Cooper on Las Vegas. In addition to his series work, Selleck has appeared in more than fifty made for TV and general-release movies, including Mr. Baseball, Quigley Down Under, Lassiter and his most successful movie release Three Men and a Baby, which was the highest grossing movie in 1987.

Selleck, born in Detroit, Michigan, is the son of Martha S. (née Jagger), a homemaker; and Robert Dean Selleck, an executive and real estate investor. The family moved to Sherman Oaks, Los Angeles, California when Selleck was growing up. His siblings include brothers Robert (born 1944) and Daniel (born 1954) and sister Martha. Selleck graduated from Grant High School in 1962.

Wendy Jane Crewson (born May 9, 1956) is a Canadian actress.

Crewson was born in Hamilton, Ontario, the daughter of June Doreen (née Thomas) and Robert Binnie Crewson. She attended Queen's University in Kingston, Ontario, where she won the prestigious Lorne Greene Award for outstanding work in the theater. She then studied at the Webber Douglas Academy of Dramatic Art in London. She was married to actor Michael Murphy in 1988 and they have two children. They divorced in January 2009 and she remarried.

Crewson joined the cast of ReGenesis in 2007 playing Dr. Rachel Woods. She also guest starred in the first eight episodes of the third season of 24, playing Dr. Anne Packard, personal physician and love interest to the President.

Margaret Grace Denig (born September 21, 1983), best known as Maggie Grace, is an American actress. Originally from Worthington, Ohio, she dropped out of high school to move to Los Angeles with her mother after her parents' divorce. While struggling financially, she landed her first role as the title character in the web-based video series Rachel's Room in 2001. She went on to earn a Young Artist Award nomination in 2002 with her portrayal of 15-year-old murder victim Martha Moxley in the television movie Murder in Greenwich.

In 2004, Grace was cast as Shannon Rutherford in the television series Lost, on which she was a main cast member for the first two seasons, winning a Screen Actors Guild Award shared with the ensemble cast. Leaving the series, Grace was keen to work more prominently in film having starred opposite Tom Welling in The Fog in 2005. She appeared in Suburban Girl, The Jane Austen Book Club (both 2007), and Taken (2008). She has the lead role of Alice in Malice in Wonderland, a modern take on Lewis Carroll's novel Alice's Adventures in Wonderland. Grace reprised the role of Shannon in two more episodes of Lost, including the series finale.

Robert John Wagner (born February 10, 1930) is an American actor of stage, screen, and television, best known for starring in the television shows It Takes a Thief (1968–70), Switch (1975–78), and Hart to Hart (1979–84). In movies, Wagner is known for his role as Number Two in the Austin Powers films (1997, 1999, 2002). He also had a recurring role as Teddy Leopold on the TV sitcom Two and a Half Men.

Wagner's autobiography, Pieces of My Heart: A Life, written with author Scott Eyman, was published on September 23, 2008.

Wagner was born in Detroit, Michigan. He is the son of Hazel Alvera (née Boe), a telephone operator, and Robert John Wagner Sr., a traveling salesman who worked for the Ford Motor Company. His paternal grandparents were born in Germany. Wagner has a sister, Mary. He graduated from Santa Monica High School in 1949.

He made his film debut in The Happy Years (1950). He was signed by agent Henry Willson and put under contract with 20th Century-Fox, where he gained attention with a small but showy part as a shellshocked soldier in With a Song in My Heart (1952). This led to star roles in a series of films including Beneath the 12-Mile Reef (1953) and Prince Valiant (1954), and White Feather (1955, with Debra Paget and Jeffrey Hunter), A Kiss Before Dying (1956, a rare villainous role) and Between Heaven and Hell (1956).