Now, in the leafy neighborhoods to the north, there are suburban-style homes, high-rise hotels, multiplex theaters, car dealerships and familiar names: Starbucks, Home Depot, Wal-Mart.
But the old city core is still a tight network of one-story façades set shoulder-to-shoulder and flush to the sidewalk, street after street, block after block, neighborhood after neighborhood.
Except for their paint jobs — mostly pastels — all the old houses looked alike to me. There was no way to tell what they were like inside, and their simple architecture made the streets look alike too — walled and blank like rows of low fortresses.
Which is exactly what they were, Heitke said.
The best example is also the oldest: Casa de Montejo, which dominates one side of the central plaza. It was completed in 1549 for the family of the city's founder, whose last descendant didn't move out until 1978.
The floor plan derives from the Romans, Heitke said: The walls are too high for intruders to scale, and everything else is hidden inside. Repeat that pattern, and the result is a grid of long, narrow houses, each with a small front on the street and only one way in.
"Close those doors up," he said, "and you're very safe."
Inside, the rooms become lower toward the back. That's where the original kitchen would have been, the servants' quarters, the toilet, the horses, dogs and chickens.
These days, that's where new owners put the swimming pool.
Some of them are snowbirds; others are absentee landlords who live in the U.S., Europe or elsewhere in Mexico. But others are full-time residents — expats who have built new lives in Mérida.
John Prentice Powell, for example, a Texas-born interior designer, painter and former model, had worked in New York and Paris before he and his partner discovered Mérida 10 years ago on a two-month-long search through Mexico.
Since then, the men have renovated about a dozen houses, some for other owners, a few for themselves, and the city is home. "I don't think I'll ever go back," Powell said.
Dave Thom, the Minneapolis dog groomer, first saw Mérida on a break from a beach vacation nearby. In 2005, he bought a 5,000-square-foot 19th-century house with original floor tiles and interior plasterwork and — not to be taken for granted here — working electricity, running water and a usable kitchen.
Thom has been renovating it ever since, supervising during his vacations from the States and trusting his workmen the rest of the time. The white-trimmed, salmon-pink façade was restored first, thanks to a city program that covers the cost of labor if the homeowner pays for materials.
The expats I met said they feel welcome in Mérida, not resented, as Americans often do in more Yankee-fied places. In this city, there are too few to make a dent: "I've heard 2,000 to 4,000," Heitke said, though nobody knows for sure.
"Mérida's not Americanized," Engle said. "It's more of an advantage to come here than to go to San Miguel. It's still Mexico."
On my last night in town — it happened to be Dec. 21, the day the 5,125-year-old Mayan calendar ended — I took a final stroll through the streets near the plaza grande. The regulars were there, but over the music from the cafes, I caught a weirder sound, high-pitched and quavering. An aggrieved soprano, maybe? Nope, just a white-haired guy in a straw hat, sitting on a box and running a home-made bow back and forth across the edge of an old-fashioned saw blade.
"My father teach me," he said in English, guessing I spoke it. "I learn by ear — all by ear! I have 1,000 songs! Listen — 'Casablanca' song!" I gave him a few coins, and the whine of the musical saw followed me for a long time as I walked away. He was playing the old song that begins, "You must remember this..." By then, I was sure I would.