With rebar that is.
Last summer I went to Mahoney State Park for horseback riding. (Yes I live in a city, and yes I paid something like $15 dollars to get a sore butt for an hour. I was coerced, but enjoyed it.)
Outside of one of their buildings they had an arch made of rebar. (click here for the best approximation I could find on the internet) I want one. I even tried to convince my dad to help me make one.
But alas, he was not excited about the idea.
Eventually I found a green wedding arch at the thrift store. I bought it. I put it together. And here it is waiting for plants to grow over it.