Landscape timbers probably won't hold the weight of the tractor. They are very weak.

Oh, I didn't know that.

Call your local utility company and see if they have any old telephone poles to sell. I know this place sells them as well, but they're not very local to you. I'm sure they could help you locate some in your neck of the woods.

Samex Crossties

Get some HD used pallet racking parts for the structure.
I have a customer who did this at his place in Meridian. Worked out good.
He drives his UTV’s and tractor over it

You should have a old style lumber yard that sells utility poles-
Like blacklands or sutherlands, those are like mini telephone poles, they are pretty stout and should do what you need and yet be affordable-

Bob if there are any Co-Op electric companies around you they will usually have old poles they have taken down. They will usually give them too you just so they don’t have to worry about disposing of them.

These are the poles a lot of folks use if they are setting up a mobil home somewhere and need to put a breaker box on it for power-

You may consider looking at rig mats. They are basically hardwood 4x4 planks bolted together, used to build a base for drilling rigs or other heavy equipment. You can often find used ones for pretty cheap around areas where there is drilling activity. This is a company I've done business with before, Quality Mats.

Thank you all for the excellent info.

They came with the property. The guy before us built the barn using telephone poles as the main supports. Guess he had leftovers.

That wooden barn has to be 75-80 yrs old now. Still in good shape. That old man knew what he was doing.

And the tractor is in the creek. Do not kid yourself

After sleeping on this; culvert is the way to go.
It’ll have the highest weight bearing capacity to simplicity of design/construction ratio.

The large metal pipe culverts are also extremely common and widely available.

Most lumber yards carry meter poles. These would be my choice over landscape timbers.