The last years of Eli Manning’s prime were wasted because the Giants could not build a wall in front of him — could not find the kind of tough, smart, gritty, cohesive offensive linemen who would give life and limb to protect him.

Once his old, reliable gang (Chris Snee, David Diehl, Shaun O’Hara, Rich Seubert, Kareem McKenzie) began growing old, Manning became a victim of too many costly personnel decisions in both the draft and free agency, and GM Dave Gettleman has only just begun the reconstruction.

Here is a look at how the Giants have sacked Manning’s chances for a third Super Bowl ring:

This was John Mara when Snee retired in June 2014: “I think Chris was everything you could ever hope for in a player: toughness, integrity and a lot of pride. Winning mattered to him. I think he set a great example for all of the other players. He’s somebody we’re going to miss very much. He was one of the greatest offensive linemen in Giants history, and he’ll be on that Ring of Honor someday.”

This was Tom Coughlin when Diehl retired in January 2014: “When I think of David Diehl, what comes to mind is his indomitable spirit. He got the most out of his God-given ability and that’s the best way that you can judge any individual. What more can you ask of the guy?’’

The Giants’ block-to-the-future plans have not gone well.

Guard Mitch Petrie was the Giants’ fifth-round pick in 2010. He started three games and lasted three years in the league. Lineman Marshall Newhouse was the Packers’ fifth-round pick. He has started 70 games.

O’Hara and Seubert had already been gone before the 2011 season, so GM Jerry Reese signed free-agent center David Baas to a five-year, $27.5 million contract to replace O’Hara in 2011. He had played one season at center with the 49ers. Baas lasted three injury-plagued seasons.

Tackle James Brewer was the Giants’ fourth-round pick in 2011. He started eight games and lasted four seasons. Lineman Marcus Cannon, diagnosed with non-Hodgkin lymphoma, slid to the fifth round. He has started 48 games for the Patriots and earned second-team All-Pro honors in 2016.

Guard Brandon Mosley was a fourth-round pick in 2012. He started one game and lasted three seasons. Guard Senio Kelemete, a fifth-round pick by the Cardinals, starts for the Texans.

Tackle Matt McCants was the Giants’ sixth-round pick. He lasted one season. Never played for the Giants. Tackle Kelvin Beachum was the Steelers’ seventh-round pick. He has started 81 games, 39 for the Steelers.

Justin Pugh was drafted in the first round in 2013. “Our type of guy,” Reese said. Versatile, tough … and injury-prone. He lasted five seasons. Bears lineman Kyle Long — a three-time Pro Bowler — was drafted one spot later.

The 2014 free-agent waters brought guard Geoff Schwartz (four years, $16.8 million), center J.D. Walton (two years, $6 million) and guard John Jerry (two years, $3.3 million). Schwartz twice broke his leg and played in just 13 games. Walton, who hadn’t played in almost three years because of a serious ankle injury, lasted one season. Jerry lasted four pedestrian seasons.

Weston Richburg was the Giants’ second-round pick in 2014. He played guard as a rookie before replacing Walton in 2015. He lasted four seasons. The Redskins drafted right tackle Morgan Moses early in the third round. He has started the past 59 games.

The drafting in the first round of Odell Beckham Jr. that year obscured a grievous mistake in the third round. Reese drafted defensive tackle Jay Bromley over guards Gabe Jackson and Trai Turner, and guard/center Brandon Linder. Jackson has started 70 games for the Raiders. Turner, a three-time Pro Bowler, has started 63 games for the Panthers. Linder has started 54 games for the Jaguars.

Free agency 2015 brought Newhouse (two years, $3 million), who would start 20 games at right tackle. And now the really bad news.

Tackle Ereck Flowers was the ninth pick of the 2015 draft, four spots in front of guard Andrus Peat. Peat, an left tackle at Stanford, is entrenched as the Saints’ starter at left guard. Flowers was forced to start at left tackle when incumbent Will Beatty tore his pectoral muscle while lifting. Flowers lasted three-plus years as a pariah.

Defensive end Owa Odighizuwa was the Giants’ third-rounder — ahead of John Miller, who starts at right guard for the Bills. Odighizuwa dressed for 18 games, no sacks. Bobby Hart was a seventh-round pick who somehow started 21 games at right tackle.

Eli Apple was the 10th pick of the 2016 draft. Reese was scared off by left tackle Laremy Tunsil’s gas mask video and was beaten to right tackle Jack Conklin when the Titans traded up ahead of him (and beaten to OLB Leonard Floyd when the Bears traded up ahead of him). see also It took awhile, but Giants' O-line isn't the worst anymore The Giants have been burned for the second-most sacks in...

Left tackle Taylor Decker was the 16th pick and center Ryan Kelly was the 17th pick. Decker has started 35 games for the Lions. Colts O-line coach Dave DeGuglielmo recently called Kelly the best center in the NFL. Apple lasted two occasionally turbulent seasons before being traded to the Saints last month.

Round 3 saw Reese draft free safety Darian Thompson over left guard Joe Thuney. Thuney was a Day 1 starter for the Patriots and hasn’t missed a game. Thompson started 17 games, recorded one interception, lasted two seasons.

Free agency 2017 brought guard/tackle D.J. Fluker (one year, $3 million), who lasted one season. Reese made tight end Evan Engram the 23rd pick. The athletic Engram has flashed promise, but he was selected nine spots ahead of Ryan Ramczyk, who played every snap for the Saints as a rookie and could be a Pro Bowl right tackle this season. Undrafted free agent Chad Wheeler, who proved better than sixth-round pick, tackle Adam Bismowaty, has replaced Flowers as the starting right tackle.

Gettleman missed on free-agent guard Andrew Norwell and pivoted to left tackle Nate Solder (four years, $62 million) and guard Patrick Omameh (three years, $15 million) and drafted left guard Will Hernandez in the second round. Omameh moved to right guard and soon out the door. Spencer Pulley, claimed on waivers Sept. 2, is the fourth center since the end of last season. Right guard Jamon Brown was claimed on Oct. 31.

“We’ve got to fix the O-Line, let’s be honest,” Gettleman said when he arrived last December.

The shame of it all is that by the time it’s fixed, the odds are stacked against Manning celebrating it.