MEXICO CITY to VILLAHERMOSA -- With few exceptions, a warlord is someone who controls a stretch of road and can, with the threat of force, extract tolls from anyone who uses it. That definition serves well in Afghanistan, where the Taliban rose to popularity in part because they subdued the warlords and made the Kandahar-to-Kabul highway something other than a suicide rally where every few miles lurked another unpredictable suzerain of the road.

By that loose definition, President Felipe Calderon of Mexico is a warlord par excellence. The distinguishing experience of riding the once lawless roads of Mexico is having to reach every few minutes for one's pile of pesos, to pass the roadblock -- excuse me, toll plaza -- of the Mexican federal government. The tolls are not huge, usually just a few dollars, but they are constant, and a constant reminder of what, in practice, is the opposite of anarchy.

Mexico's highway system, like the American one, seems built with strategic threats in mind. But the strategic threats in Mexico are internal. So whereas Eisenhower championed the Interstates to keep movements of men and materiel possible in case of foreign invasion, in Mexico the overwhelming role of the highways seems to be one of limitation and control. Outposts of the Mexican government include not only the ubiquitous toll plazas but also every filling station (PEMEX is the state-run gas monopoly). Rather than spoiling a traveler for choices for food and roadside recreation, and providing every few miles a rest area with fast food, truck-stops, and giant balls of string, here in Mexico the highway are chutes that lead from town to town insistently, like the highway to West Berlin, with few chances for exit or distraction along the way.

Now that I have reached Tabasco and Chiapas -- the states that were Graham Greene's destination, and that have recent memory of uprising -- the reason for this level of control is clearer. The toll plazas function more like roadblocks than some would care to admit, because they accomplish the simple goal of stopping traffic, taking money (legitimately), and allowing the warlord to peek into your vehicle and protect his interests. Here in Tabasco, or more properly on the road to Tabasco from Veracruz, I met my first real checkpoints and signs of military influence: dozens of olive-colored trucks along the road, filled with soldiers, and at key intervals a speedbump and a crowd of men with rifle vests and automatic weapons. In Chiapas, where the military presence is thinner, as soon as you stop seeing roadblocks you start getting signs of defiance, like these:

Graham Greene faced a search on arrival in Tabasco as well, and like him I found it best to forget all my Spanish and let the authorities come to the conclusion that it would be easier to let me pass than to bother pantomiming to me their intention to search through my dirty laundry for weapons and drugs. Being searched is rarely pleasant, though it is at least a slight feeling of homecoming and familiarity to know that at least in this respect the Mexico of Graham Greene's time bears a resemblance to today's.