Mr Martinez and fellow Indians, in two-weekly shifts, have been camped on the square in the heart of the capital for more than four years, protesting against the takeover of their land by wealthy white or mestizo (mixed-race) caciques (landowners).
'Our problem is the same as in (the state of) Chiapas. The caciques have taken over our plots. They have pistoleros (gunmen), paramilitary forces, even the army to support them. Last week, after the Chiapas troubles, the army sent tanks to our lands. But our only arms are our work tools - machetes and scythes,' he said.
Mr Martinez belongs to the Emiliano Zapata Eastern Mexican Democratic Front, an open Indian campesino grouping of Nahuatl Indians from the region they knew as Las Huastecas long before it was broken up into the present-day states of Veracruz, Hidalgo and San Luis Potosi. It is one of hundreds of such groups throughout Mexico, many of them bearing Zapata's name. Their claims for land, true democracy and equal rights have gone largely ignored by Mr Salinas's government. Some have been bought off to ensure they vote for the right candidates.
The New Year uprising in Chiapas, by the Zapatista National Liberation Army (EZLN), may force their voices to be heard. For the first time in years of public protest, Mr Martinez's group was called in by the Interior Ministry last week to voice its complaints.
The key question here is whether other groups might follow the example of the EZLN, thought to be based on a previously open group called the Emiliano Zapata Independent National Campesino Alliance (Anciez), in taking up arms. There are clear signs that diverse Indian groups are seeking to unite and win the support of left-wing workers, students and intellectuals in the light of the Chiapas peasant guerrillas' humbling of Mr Salinas's government. Around 140 Indian peasant groups in Chiapas alone announced at the weekend they would form an 'autonomous, state-wide organisation'.
The EZLN has demanded Mr Salinas's resignation and a transition government that would end 65 years of one-party rule by his Institutional Revolutionary Party (PRI). It has also pledged to march on Mexico City, a threat that may at first have sounded rhetorical from a few thousand southern peasants. But then few Mexicans would have believed in 1910 that Zapata and a bunch of ragged peasants would eventually ride or walk into the mighty capital in 1914 as wealthy citizens hid from sight, decades of dictatorship finally smashed. The EZLN threat would be conceivable only if Indian peasant groups from around the country, with student and worker support, joined in the Chiapas battle cry.
For the first time in its long history, there is a growing sense here that the PRI may soon go the way of other institutions previously thought indestructible, such as the Berlin Wall and the Soviet Union.
The Mexican army is taking no chances. There was a car bomb in Mexico City earlier this month. Tourists who wanted to visit the National Palace on the Zocalo (main square) at the weekend, where thousands usually flock daily to see Diego Rivera's magnificent murals, found the gateway blocked by a force of combat-ready troops. Military helicopters circled the city.
Mr Martinez's group first set up camp in the Zocalo in the summer of 1989. They were forcibly removed later that year by no-nonsense granaderos (riot police). Their place in the square has been successively taken by many other groups seeking basic rights. Yesterday, it was Indian sugar estate workers from Tabasco who had set up camp facing the National Palace, which is the President's official residence even though he lives and works elsewhere. Sooner or later they, too, will be moved on by the granaderos.
Despite the renascent ghost of Zapata, the new imagery being evoked here is as much that of Mexico's independence from Spain in the early 19th century. One night in September, 1810, a Catholic priest called Miguel Hidalgo rang the church bells in the mainly-Indian town of Dolores 120 miles north- west of here, and made the grito (cry) of insurrection, seen as the spark that finally led to independence in 1821.
In Chiapas last week, Bishop Samuel Ruiz of San Cristobal de las Casas, a longtime fighter for the rights of Chiapas's majority Indian population, said at a Mass almost within earshot of army troops: 'A cry has risen up, a cry that lamentably has caused loss of life among the army, the civilian population and the brother insurgents.'
The word 'brother' was the key to Bishop Ruiz's sentiments. Those who know him say he sees the Chiapas uprising not only as an inevitable result of the Indians' hunger and desperation but as the spark that could be the beginning of the end of the PRI's long monopoly.
Mexico's main opposition, the Party of the Democratic Revolution (PRD), whose candidate in next August's presidential elections, Cuauhtemoc Cardenas, believes he was robbed of victory in the 1988 elections through fraud, also sees the Chiapas uprising as the spark that could lead to the fall of the mighty PRI. In the words of the PRD leader, Porfirio Munoz Ledo, 'after the Chiapas conflict, the final consequence can be nothing other than the democratisation of the country'.
The writer Carlos Fuentes, in an article in the daily El Norte, took a similar tack. 'The insurrection in Chiapas has confirmed a national suspicion: without political reform, economic reform is fragile, in fact deceptive. The Mexican political and economic system, anti-democratic and unjust, is partly responsible for the Chiapas uprising.'