ARLINGTON, Va. -- He was looking for a challenge and for a way to honor service members.

Tom Sandler is a retired Army Veteran and continues to help serve veterans.

He came up with an idea to further his service after running several marathons with a friend.

What if they walked between the gravesites of decorated Marine Chesty Puller and that of decorated soldier Audie Murphy?

His friend, also a veteran, agreed and “we talked about it and talked about it and nothing ever came of it,” Sandler said.

That was two and a half years ago.

In April, Sandler was running the Boston Tough Ruck run alongside fellow Army Veteran Susan Timko Muerdler. The challenging 26.2 mile course is completed with a ruck and honors fallen service members.

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There, Sandler asked Muerdler if she would be interested in his idea. She said yes. But like with his friend from years earlier, nothing solid came of it.

It wasn’t until Sandler was in church that he heard a story that inspired him. A passage from the Bible describes Jesus telling a man who doesn’t believe he can stand to just "get up and walk." For Sandler, who said he “just kept making excuses,” this was the push he needed.

Sandler and Meurdler set out on Friday from Chesty Puller’s gravesite at Christ Church Cemetery in Middlesex County, Virginia towards Audie Murphy’s gravesite at Arlington National Cemetery in Arlington, Va.

Between the two of them, like a relay, they pass the American Flag.

“One flag, hero to hero,” Sandler explained. Once they reach Murphy’s gravesite, they plan to fold the flag along with a Navy veteran friend and present it to Murphy.

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But, that won’t be until they hike over 150 miles. And the walk is grueling. The day that the two set out, a heat wave began in the area, driving temperatures near 100 and the heat index well-over. But with ruck and American flag in tow, the two kept on.

“Sunrise, sunburn, sunset, repeat,” Muerdler joked in a Facebook Live on Friday.

It’s more than just a hike, too. According to a GoFundMe set up by the pair, they are also raising money for several different veteran-focused charities: Middlesex Museum, Operation 99, Leashes of Valor, Restoration of the VFW Post 3103 Building in Fredericksburg, N Stafford JROTC, and Operation Ward 57.

On Monday, the pair had reached Stafford, Virginia after walking 23 miles and spent some time surrounded by friends and family, some of whom are following the two and some who just came out to support them. They also sold shirts to pay for gas (Sandler explained that they take turns driving an RV ahead of the other while they hike) as well as to raise money for charity.

On Tuesday, they plan on visiting the Marine Corp Museum before making their way to their final destination in Arlington National Cemetery. They will complete the mission on the Fourth of July.

“It’s just an amazing adventure to honor our heroes,” Sandler said. You can follow their journey here on their Facebook page.