By Martin Murphy
BBC Americas analyst
Colombia's President Alvaro Uribe is leading a nationwide protest against kidnapping, a week after the deaths of 11 provincial lawmakers held by rebels.
After 40 years, Colombians are saying they have had enough
The protesters are also demanding the release of more than 750 hostages still in the hands of the Revolutionary Armed Forces of Colombia, or Farc.
The protest comes as talks between the government and the Farc are deadlocked.
The murder of the politicians last week in unclear circumstances has further increased mistrust between both sides.
The Farc said the men, held hostage for five years, died in crossfire during a military raid on a guerrilla camp.
The Colombian government has denied that any military operation took place and accused the guerrillas of killing the men in cold blood.
The marches, beginning at midday (1700 GMT), are against the rebels, but they also send a clear message to the government that an agreement is needed to free the hostages.
The rebels want the government to hand over control of two towns in the south-east of the country and have demanded the release of their imprisoned compatriots.
Mr Uribe has recently freed some rebels but he opposes handing over any territory to them.
After more than 40 years of armed conflict and several failed peace negotiations, Colombians seem to be telling the rebels and the government that they have had enough.