The collapse of a section of cliff on the morning of August 21, 2009, caused the death of five people who were on holiday in the Algarve.
The case against the State, now being heard in court, is that the dead and injured were unaware of the risk of collapse at Maria Luísa beach, Albufeira.
The rock that sheared off from the cliff was ten metres high and six metres in diameter, weighing several tons, and killed five people, four of them from the same family.
Vítor Sousa, who was seriously injured, told a court that although he saw a "small signal" that there was impending danger, he did not interpret it as constituting a real danger of collapse.
Following the Maria Luisa beach tragedy, the Portuguese Environment Agency (APA) carried out 16 controlled landslides and boosted signposting to avoid similar occurrences.
The then APA director, Sebastião Teixeira, presented a report in 2009 that referred to the "unpredictability and instant nature" of the collapse which had characteristics, "very similar to the dangers associated with earthquakes."
Maria Luísa beach is categorised as having "high" and "very high" vulnerability, according to Óscar Ferreira and Alveirinho Dias, researchers at the University of Algarve, who said that when the tide comes in, beachgoers huddle near the bottom of the cliff and ignore warning signs.
Ferreira and Dias argue that the State "can not eliminate or minimise, all the risks without jeopardising individual liberties in a dangerous and perhaps unacceptable way."
Alerts for dangerous situations should be part of the information to be given to citizens, so that they are responsible for their own actions.
The researchers stated that in the region, "30% of the beaches under cliffs in the Algarve have very high vulnerability," added to by construction at the top of cliffs and vehicle traffic."
The case continues.