SHEATHED IN SMOOTH, tobacco-colored leather, the instrument that once pinned vast chunks of the Arab Middle East to colonial Britain's map was cradled in my right hand. It was densely heavy—cool to the touch—and its burnished brass and thick glass crown glinted in the afternoon light.

Called a Verners–Pattern VII, it was a field compass made in Switzerland in 1915, identical to thousands used by British officers during World War I. But this one was unique, because the name embossed into its leather case—T.E. LAWRENCE—meant that it had once been owned by Lawrence of Arabia.

Standing at the back of Christie's auction house, in London (and watched over by clerks and security cameras), I imagined the compass's luminous needle directing Lawrence across the northern desert of Arabia in July of 1917. That's when, working as a British intelligence officer, he'd led a scruffy band of Arab rebels through the unmapped sands, sneak-attacking the Ottoman Turk stronghold of Aqaba from behind. The ensuing rout helped drive the Ottomans into collapse, birthing the modern Middle East.

"Lawrence's compass," I said. "That's so... It's... Wow."

Sure, it was only a hunk of magnetized alloy, but to me it gave off a tangible buzz. I refastened the leather flap and placed the compass back in its velvet-lined wooden box, nestled between Lawrence's pocket watch and his silver cigarette case.

I was being watched for a good reason: All three relics had just been gaveled off by Christie's—one of the world's leading art-and-antiques auction houses—to an anonymous bidder, who paid £254,000 (about $480,000) for the set. And the bidding wasn't over. Up a grand flight of stairs from where I stood—in a stately, cream-painted hall on the second floor of the Christie's building in London's exclusive St. James district—the morning session of the annual Exploration and Travel Sale was still going strong. Other personal items of Lawrence's were on the block, and I could hear the sale's low, elliptical murmur in the background, punctuated occasionally by the crack of the auctioneer's hammer. For me, though, the compass was the morning's high point, and I held it a minute longer, relishing its complicity in Lawrence's audacious, humanly flawed, and world-altering contribution to history.

Then I handed everything over to a clerk, who whisked it off to a packing area. It was quite a feeling. But, looking back, I have to wonder if I put more vibrational energy into the compass than it put into me. Three weeks after the auction—in a claim that's a first for such a sale at Christie's—it would be challenged as a possible fake.