SAN DIEGO -- Officially, Petco Park opened in 2004. In reality, the first bricks were unknowingly laid nearly a century before that.

What's the defining feature at the Padres' downtown yard? The Tony Gwynn statue comes to mind. As does the park beyond the outfield, the right-field deck and the right-center-field beach area.

But if it's one singular feature, it has to be the Western Metal Supply Co. building, a ballpark fixture unlike any in baseball. Built in 1909, the four-story brick structure set the baseline for the construction of the entire stadium.

The historic 51,400 square-foot warehouse once housed San Diego's Western Metal Supply Co. and was declared a historic landmark by the city in 1978. When the Padres began to lay out their new East Village ballpark, they started in left field -- where the building would loom large over the field of play, 336 feet from home plate.

In one of the stadium’s unique quirks, there is no foul pole in left field. The southeast corner of the building does the trick. Any ball that hits the eastern wall is a home run. Any ball that hits the southern wall is ruled foul. The painted yellow line that graces the corner? For show.

The building was designed by architect Henry Lord Gay, and it housed the Western Metal Supply Co., run by brothers Bernard and George McKenzie beginning in the late 19th century. Originally, the company produced mostly materials for wagonmakers and blacksmiths, but it grew into one of the city's prominent businesses until its shutdown in 1975.

When the Padres set about construction in the East Village, they not only preserved the landmark, but they upgraded the building and made it a feature. Three decks protrude from the east-facing side for fans to enjoy games from. The rooftop, 80 feet above ground, is also fan accessible, and the first floor hosts the Padres' team store.

In its existence, the Western Metal building has seen its share of memorable moments:

• Phil Nevin launched the first home run into the building on April 15, 2004.

• When the Padres clinched the 2005 National League West title, the team unveiled a banner that covered the words "Metal Supply Co." atop the building. It read instead: "Western Division Champs."

• Giancarlo Stanton won the 2016 Home Run Derby at Petco Park, peppering line drives off all four levels of the building.

• Later in 2016, Hunter Renfroe became the first player to homer onto the roof of a building during a game when he took Dodgers right-hander José De León deep. Renfroe did so again the following summer -- against Mets ace Jacob deGrom.

• On Aug. 27, 2020, Renfroe was joined by Fernando Tatis Jr. as the only players in ballpark history to homer onto the roof -- a truly titanic feat, considering the elevation needed to lift a baseball more than 80 feet high at least 336 feet away from home plate.

• Wil Myers' go-ahead homer in Game 2 of the 2020 Wild Card Series against the Cardinals hooked sharply down the line in. When the ball caromed off the eastern wall, it was officially a home run. The Padres took the lead in dramatic fashion, and they went on to win the game and their first playoff series in ballpark history.