Two more ancient Roman walls collapsed in Pompeii today following the collapse of another yesterday and the ruin of a frescoed house last month.

Experts blamed persistently heavy rains which have lashed the site in recent weeks, wearing away the ancient mortar between the stones.

Neither wall had frescoes or murals on it according to curators at the site.

"These things can happen in a vast archaeological site that is 2,000 years old, especially considering the weather conditions we've had over the last few days," said Jeannette Papadopoulus, superintendent at the site.

Yesterday, a 12-metre (40-foot) long wall fell behind the House of the Moralist, so-called because the owner wrote rules of etiquette for visitors on the walls of his home including "Let water wash your feet clean" and "Take care of our linens."

The collapse into rubble of Pompeii's House of the Gladiators on November 6 sparked sharp debate over the future of Italy's cultural heritage.

Government officials denied the incident was due to cuts in the culture budget and blamed local management problems at the site.

Once a bustling city, Pompeii was entombed by the massive eruption of nearby Mount Vesuvius in AD 79, but was partly excavated and attracts thousands of visitors every year to one of the best-preserved ancient sites in the world.

In July 2008 Italy declared a "state of emergency" for Pompeii, saying it had fallen into serious disrepair.

Culture Minister Sandro Bondi warned on Tuesday against "useless alarmism" and said the situation in Pompeii was being constantly monitored by experts