What is the difference between a coastal fort and a fortlet?

It is above all a question of scale and function. A fort is a self-contained work of medium size, with a permanent garrison and significant firepower. A fortlet is a smaller structure, sometimes no more than a battery with a redoubt, intended to hold a secondary point — a cove, a landing beach or an exposed stretch of coast — and to operate in concert with larger fortresses nearby.

Why were so many forts built along the Portuguese coast?

Portugal has a long and exposed coastline, and for centuries it was threatened by North African and French corsairs, by enemy fleets and by the risk of landings. The river mouths — above all that of the Tagus, the access to Lisbon — were critical points. After the Restoration of 1640, the Crown multiplied forts and batteries to close off these entrances and watch over beaches where landings were easy.

Do coastal forts still exist today?

Many have survived and are classified as heritage. Some retain a military use, others have been converted into lighthouses, museums, inns or cultural venues. Several lie in ruin or are threatened by marine erosion, but as a whole they continue to mark the Portuguese coastal landscape strongly.

Coastal Forts and Fortlets

Anyone travelling along the Portuguese coast comes across, at almost every cape and every river mouth, the remains of a defensive line raised over the course of three centuries. These are the coastal forts and fortlets: works of small and medium size, scattered along the seafront to guard coves, close off river mouths and watch over the beaches where an enemy might land. On their own they were modest; together they formed a system that defended the coast and, above all, the sea approach to the kingdom’s capital.

An unbroken line along the sea

Unlike the medieval castle, conceived to withstand a prolonged siege, the coastal fort was designed for crossfire and for surveillance. Its purpose was to prevent enemy ships from forcing a river mouth or troops from coming ashore on an unguarded beach. Hence its characteristic layout: relatively low structures, with a polygonal plan adapted to the terrain, their batteries oriented towards the navigation channel and able to cross fire with neighbouring positions.

This logic explains the density of works at sensitive points. At the mouth of the Tagus, the entrance to Lisbon was defended by a rosary of forts and batteries that covered the channel mutually from one bank and the other, headed by the imposing Fortress of São Julião da Barra, the “shield of the kingdom,” begun as early as the 16th century under King João III. Among these positions, the smaller fortlets plugged the gaps that the larger fortresses could not reach.

A coastal fort rarely fought alone. Its worth was measured by the reach of its neighbours: to defend the coast was to design, point by point, a web of fire that would let neither a ship pass nor a beach lie open.

From the watchtower to the bastioned design

The defence of the coast began, in the Middle Ages and the early Modern period, with towers and watchtowers that raised the alarm against corsairs. With the spread of artillery, however, the high wall became vulnerable, and military design evolved towards the bastioned system: plans of bastions, curtains and ravelins of low profile, able to resist the cannon and to sweep the surrounding ground. The coastal forts adopted this same principle from the great bastioned fortresses, albeit at the reduced scale that their function required.

The great impetus came with the Restoration of 1640. Faced with the need to secure the coast against Castile and against piracy, the War Council of King João IV ordered the raising, within a few years, of a remarkable group of forts between Cape Roca and Belém and along the entire seaboard. Many made use of stone from ruined buildings nearby; the Fort of São João Baptista, on the Berlengas, raised from 1651, rose upon the remains of a former island monastery to guard that archipelago, exposed to North African and French corsairs.

Function, decline and new life

Over the course of the 17th and 18th centuries, the network spread to the whole country and to the Atlantic world — from the Azores and Madeira to the strongholds of Africa and Brazil — always with the same grammar of batteries and redoubts beside the surf. The Algarve, the Sado estuary, the mouth of the Douro and the river mouths of the North received their own forts and fortlets, articulated with the inland fortifications in a single strategy for the defence of the territory.

With the end of the threat of invasion by sea and the transformation of modern warfare, these works lost their military use. Some were converted into lighthouses, others into inns, museums or cultural venues; many were left abandoned, and not a few are today threatened by the very erosion of the sea they once watched over. To recognise this ensemble — and to visit it, as proposed by military tourism among Portugal’s fortifications — is to read in stone the country’s long relationship with the ocean: the same sea that opened the expansion was also the frontier that had to be defended, bay by bay, along the entire coast.