Some 1,000 demonstrators from rural Central Tunisia, calling for the resignation of the transitional government, reached the capital on Sunday.
The marchers, from a poor farming region where an uprising against authoritarian rule began in December, called for the resignation of a government put in place after the ouster of President Zine El Abidine Ben Ali.
"The people have come to bring down the government," they chanted as they marched through the centre of Tunis.
The "Caravan of Liberation" set off on Saturday from the town of Menzel Bouzaiane, where the first victim of a bloody crackdown on protests against Ben Ali was killed in December.
"We have come. To bring down the rest of the dictatorship," said Mohammed Layani, an elderly man draped in a Tunisian flag.
There have been daily protests in recent days calling for the resignation of Prime Minister Mohammed Ghannouchi, who has been the premier since 1999 and has stayed on despite the downfall of Ben Ali.
Protesters have also called for the break-up of the ex-ruling Constitutional Democratic Rally, the RCD, which has dominated Tunisian politics for decades.