A larger anti-Farc rebel group protest was held in Colombia and in cities across the world in February.
Colombia's so-called "paras", including groups such as the United Self-Defence Forces of Colombia (AUC), were largely formed as private security forces in the 1980s to protect wealthy Colombians and to combat groups such as the Revolutionary Armed Forces of Colombia (Farc).
However, the groups have been blamed for scores of massacres, kidnappings and disappearances, and the AUC has been designated a terrorist group by the US and the European Union.
More than 30,000 paramilitary fighters have been demobilised and decommissioned since 2004 in a peace deal.
Thursday's rally came amid a diplomatic crisis in which Ecuador, Venezuela and Nicaragua have all cut diplomatic ties with the Colombian government following a Colombian army raid this weekend in Ecuador which killed a senior Farc commander.