Assaulted by thousands gasping for air in summer and once by Roman emperors the coastline of the giant province of Rome, has nevertheless long been a dicey place, tinged with scandal.

Over the past few years whisper those in the know it has become the target of gangs from the expanding Neapolitan Camorra and the dumping-ground of Albanian traffickers for illegal immigrants smuggled ashore along the Adriatic coast and then over the Appenines.

A major political scandal blew up in the 1950s when the near-naked corpse of a seductive Roman girl, Wilma Montesi, was found on the beach of Torvaianica south of Ostia. Among her many acquaintances was the son of one of the most prominent Christian Democrat leaders of the day, then foreign minister Attilio Piccioni, whose career was shattered but the case was never solved. Two decades later, in 1975, the poet and film-maker Pier Paolo Pasolini was butchered to death one night on waste ground near the mouth of the Tiber. That mystery has remained unresolved as well.

But once Romes coastline was a far riskier place. For over ten centuries it was prey to repeated incursions by Saracen raiders or Barbary pirates from north Africa.

To parry their persistent wasp bites, the coastline soon turned into a front line, dotted by as many as 20 defence towers, forts or castles, erected mainly in the 16th century on the orders of cardinals or popes intent on safeguarding the then growing temporal power of the papacy. Fourteen still stand, punctuating a coastline stretching from the seaside of the old Etruscan city and burial ground of Cerveteri to the north of Rome down to the so-called Tower of Asturia (Torre Asturia) to the south, easily the most evocative and secret of all the forts.

Totally isolated amid almost impenetrable woodland, it rises out of the sea south of Nettuno, a four-walled mediaeval fortress with a central watch-tower connected to the shore by a narrow causeway, with the outline of submerged ancient Roman fish tanks showing through the water. And secret it is because cars can get nowhere near it, access to the magnificently deserted beach it guards calling for an expedition through shrubs and undergrowth. It dates from 1193, which was when the Counts of Tuscolo plonked it there to deny freedom of pillage to the Saracens who infested the coastline through previous centuries. This was the isolated hideout of the fugitive Corradin, the adolescent who was the last in line of the great German Hoenstaufen rulers of the Holy Roman Empire. But Corradins Italian protector betrayed him to the French, who executed the hapless lad in the marketplace of Naples.

The most ponderous of these coastal forts is the massive fortress of Nettuno (Fortezza di Nettuno) in Nettuno itself, a stones throw from the towns midget mediaeval quarter, where to watch the action you dine on outside tables in a main square that fair hogs the adjective picturesque. As for the dour fortress with its bulging bastions, commissioned by Pope Alexander VI from the with-it renaissance architect Giuliano di Sangallo, it soon became the military kingpin of the whole coastline.

Cheek-by-jowl with Nettuno is ancient Anzio, founded, some claim, by a son of Ulysses and the sorceress Circe and the birthplace of both Nero and Caligula. It too once boasted a fortress, until this was blown away by British naval gunfire in 1813 during the Napoleonic turmoil.

For anybody living in Rome, the most accessible and by far the finest example of a coastal defence fort is the great turreted renaissance castle facing the entrance to the excavations of Ostia Antica, which as simple Ostia (from the Latin Ostium = mouth), was once the most heavily-attacked of all the Saracen objectives. In 849 AD, the Saracens sacked Rome itself; and continuing raids thereafter were only brought to an end when, three years later, a pope organised an alliance with Amalfi, Gaeta and Naples which trounced the north Africans at a big sea battle at the mouth of the Tiber, a victory alluded to by Raphael in La Cacciata di Eliodoro in the Vatican Museums.

Then it was the turn of home-grown Italian strongmen and others to knock off Ostia. The risposte to such a habit was the present castle, once on the very bank of the Tiber, conceived by another renaissance designer, Baccio Pontelli, and finished under the so-called warrior pope, Julius II, while he was still a cardinal in 1484.

Then the great brick castle with its moat and drawbridge lost the whole point of its existence when in 1557 the capricious Tiber switched its course in a flood, leaving the elegant castle and its surrounds to turn into a malarial bog that remained such for 300 years.

The coastal defence was then allotted to a new tower, Tor S. Michele, a kilometre north-west of the old castle. Ordered by the garrison commander of Ostia, its design was entrusted to the great Michelangelo himself, a stylish, three-tiered octagonal affair, though, oddly for the great man, he left it without either crenellations or gun-sights, which was why it fell to the very first units to attack it three Corsair pirate vessels from Tunisia. Its doom was sealed and in the end it served as a crude control tower in the 1920s for seaplanes coming in to land in the old mouth of the Tiber, or the Fiumara Grande as it is still called today.

Today, it is a forlorn landmark, marooned in a desolate no-mans land littered with fly-by-night car-body workshops, mattress-makers and the like. Now it has a neighbour: a sad little memorial garden commemorating Pasolini, with stone quotations from his poems and benches surmounted by a small abstract monument. It was inaugurated by the Rome city council in November last year on the very spot where the artist was murdered. According to Eugenio Cerini, chairman of the Ostia tourist board, there is now a sketch of a project for the disused Tor S. Michele to be converted into a more fitting museum devoted to the whole opus of Pasolini.

Why has it taken so long?

His was for many an unwanted, troublesome (scomoda) voice when he lived, replied Cerini, presumably meaning that accommodating such a voice has needed time.

Ostia (Giulio II) Castle, Mon-Fri 09.00-12.45, Tues and Thurs also 14.30-16.15. Only 15 visitors at a time, shown around by a guide. The Pasolini Memorial, Via del Idroscalo opposite Atlantico 1 stop for buses 014 and 015.