We hit the spikes on Interstate 40 East in Texas, soon after the second-largest freestanding cross in the Western hemisphere dropped over the horizon and disappeared from our rearview mirror, along with the giant thing crucified on it. (All the faded tourist-trap signs claim that cross is the largest, but I look into these things, and I know the cross in Effingham, Illinois actually has a wider armspan.)

Our car hit the spikes at speed. Four blowouts and several seconds of terror later I gave up on the regular brakes and yanked up the emergency. The car spun, screeching, and settled mostly on the shoulder, pointed back west, the low sun glaring in our eyes.

Tana got out and I followed, trembling, as she knelt and pried a metal spike from the deflated rubber of one tire. It looked like an oversized jack, something a child would play with, but with sharp points. “Caltrops,” she said, then looked up. “They’re all over the road back there.”

“So, what’s that, medieval? To stop heavy cavalry charges? They’re for maiming horses, not cars, right?”

“They were used even earlier, in Roman times, against horses drawing chariots. I think radical environmental activists used them into the modern era, but I was a Classics major, so it’s outside my area. Could be from almost any time, really.”

I took a shotgun from the back seat, and handed Tana a crossbow. I heard whoops coming from far up the highway to the east, but couldn’t make out enough of the language to guess their origin. If they were moderns, the shotgun could help. If they were from a civilization that predated firearms, the shotgun would just be an unwieldy club. Ever since the Disaster — or, as they call it where I’m from, The Shake-Up — time’s been funny. Highwaymen bring the technological limitations of their own eras with them. “Did the Romans even have crossbows?”

Tana shrugged, loading a bolt. “They had ballista. Close enough.”

We put our backs against the car and watched our ambushers, rapidly approaching specks charging down the blacktop. “We had some good times, didn’t we?” I said. “I mean, we — ”

“Hey,” she said. “You know, there’s hundreds of caltrops scattered on the road back there. Why don’t we walk real carefully and get on the other side of them? I’d like to see these guys rush us then, with the sun in their eyes and spikes in their way. We might have a chance.”

That’s why I love Tana. She’s way smarter than me. Without her, I would have died the first time I tried to use a chainsaw against a caveman.