It began in June with a large cardboard box, just roomy enough to house my wiry eight-year-old son, Nathan, and a scrap of old tweed carpeting.
''The fort,'' as Nathan dubbed it, was expanded throughout his summer vacation to include several new rooms, each fashioned from salvaged appliance boxes of various shapes and sizes. By the time it was finished, the fort was a veritable castle, sprawling like a giant corrugated snake across one side of our front lawn.
Other young, aspiring architects in our neighborhood added their own flourishes - round windows, paper awnings and flags, plastic pipes and tubes. (Whether these served functional or aesthetic purposes, I'll never know.)
This cardboard Xanadu became something of a local landmark. It was such hot property, in fact, that you had to write your name on the official sign-up sheet to be admitted inside, rather like the exclusive restaurants lining Main Street downtown.
But since we live on a corner lot in a manicured Midwestern suburb, I worried that our neighbors would object to the ever-growing mountain of boxes in our yard. If you had no imagination and didn't know you were looking at a playhouse, you might have guessed that we were being careless about storing our trash.
But nobody uttered a complaint. Other parents who had watched the fort's progress were amazed to see that something as simple and economical as a stack of boxes could keep so many children amused for so long. One afternoon a local building contractor even stopped his truck to admire the fort's whimsical design.
''Hey there! That's quite a place!'' he called out to Nathan and his friends. ''Are you selling space in your cardboard condo?'' But my son earnestly replied that he wasn't looking for more tenants.
''Every spirit builds itself a house, and beyond its house a world, and beyond its world a heaven,'' wrote Ralph Waldo Emerson.
We are born with the desire to create a home, to build our own retreat. And while home can mean something different to everyone you ask, the need for a sense of place is universally human. To a small boy, any discarded carton contains unlimited potential for a playhouse or a fort - a room of his own.
BUT to the homeless man who camps near the railroad tracks on the outskirts of our town, a cardboard box provides temporary shelter from the elements and might be his only refuge.
Nathan and I first spotted the homeless man's shelter a few weeks after the fort was built. We were heading for our favorite fast-food restaurant downtown, taking our time as we walked along a gravel service road flanking the railroad tracks.
The two of us noticed a crude assemblage of large boxes almost hidden behind a cluster of overgrown bushes and weeds. Torn blankets and soiled clothing were strung on branches nearby, while long sheets of blue plastic encircled the base of the boxes like small rivers. Right away, Nathan noticed that the shelter bore a remarkable resemblance to his cardboard fort back home.
''What is all the plastic for?'' Nathan whispered as we walked past the encampment. I explained that the man probably used the plastic to keep the boxes dry when it rained.
''But why does the man live there instead of in a real house?'' he pressed in disbelief.
I grappled for an explanation. How do you define what it means to be homeless to an eight-year-old child who plays in cardboard boxes all day, then sleeps at night in a bed with freshly laundered sheets?
Following a heat wave later that week, a powerful evening storm rolled in. It brewed so quickly that I didn't have time to pull Nathan's fort into the garage.
Inevitably, the next morning, my son discovered that his cardboard heaven was scattered across the lawn. Even ''the turret,'' a sturdy refrigerator carton in its previous life, had toppled like an uprooted tree among the soggy ruins.
At first I was relieved to think I could finally disarm the army of boxes that had taken over our yard. But I could see that my son was fighting tears as he tried to salvage parts of his creation. Suddenly, an immaculate lawn seemed very unimportant in the grand scale of things.
I put my hand on my son's shoulder and told him that I, too, was sorry that the fort had collapsed. Together we folded the sheets of rain-soaked cardboard and piled them near the trash in our garage.
Since then, school has started again. But we haven't discarded a cardboard box without seriously considering its possibilities.
And we often wonder about the homeless man who had set up camp near the railroad tracks. The last time we walked there, we noticed that his home, like Nathan's fort, had collapsed in the hard summer rain.