The distinctly dubious Diocletian provides a distraction en-route to the Fortunate Isles.
Ptolemy placed the Fortunate Isles off the West coast of Libya Inferior.
The Fortunate Isles or Isles of the Blessed were semi-legendary islands in the Atlantic Ocean, variously treated as a simple geographical location and as a winterless earthly paradise inhabited by the heroes of Greek mythology.
Flavius Philostratus’ Life of Apollonius of Tyana (v.2) says,
“And they also say that the Islands of the Blessed are to be fixed by the limits of Libya where they rise towards the uninhabited promontory.”
Ptolemy used these islands as the reference for the measurement of geographical longitude and they continued to play the role of defining the prime meridian through the Middle Ages.
Wikipedia – Fortunate Isles
Philostratus or Lucius Flavius Philostratus (c. 170 – 247/250 AD), called “the Athenian”, was a Greek sophist of the Roman imperial period.
Wikipedia – Philostratus
Apollonius of Tyana (c. 15 – c. 100 AD), sometimes also called Apollonios of Tyana, was a Greek Neopythagorean philosopher from the town of Tyana in the Roman province of Cappadocia in Anatolia.
Wikipedia – Apollonius of Tyana
Claudius Ptolemy (c. 100 – c. 170 AD) was a mathematician, astronomer, natural philosopher, geographer and astrologer who wrote several scientific treatises, three of which were of importance to later Byzantine, Islamic and Western European science.
Wikipedia – Ptolemy
Modern Earth Scientists have problems finding [amongst many other things] the Fortunate Isles because they can’t find a longitudinally aligned island chain off the West coast of North Africa.
Modern Earth Scientists can’t believe / accept / understand [delete as appropriate] the straight-line Fortunate Isles have morphed into an island arc during the Current Era.
It’s possible the Madeira, Canary and Cape Verde volcanic chains are trailing edge artefacts attached to North Africa by lava tubes containing friction heated molten rock.
Malaga Bay – The Senegal Swing
Modern historians have problems finding the Fortunate Isles because they’re told Libya Inferior didn’t have a Western coastline.
Wikipedia – Diocese of Egypt
Modern historians are given the impression Libya Inferior only had a Northern coastline facing the Mediterranean Sea.
Marmarica in ancient geography was a littoral area in Ancient Libya, located between Cyrenaica and Aegyptus.
It corresponds to what is now the Libya and Egypt frontier, including the towns of Bomba (ancient Phthia), Timimi (ancient Paliurus), Tobruk (ancient Antipyrgus), Acroma (ancient Gonia), Bardiya, As-Salum, and Sidi Barrani (ancient Zygra).
The territory stretched to the far south, encompassing the Siwa Oasis, which at the time was known for its sanctuary to the deity Amun.
The eastern part of Marmarica, by some geographers considered a separate district between Marmarica and Aegyptus, was known as Libycus Nomus.
In late antiquity, Marmarica was also known as Libya Inferior, while Cyrenaica was known as Libya Superior.
Wikipedia – Marmarica
Late antiquity is a periodization used by historians to describe the time of transition from classical antiquity to the Middle Ages in mainland Europe, the Mediterranean world, and the Near East. … Precise boundaries for the period are a continuing matter of debate, but Brown proposes a period between the 3rd and 8th centuries AD. Generally, it can be thought of as from the end of the Roman Empire’s Crisis of the Third Century (235–284) to the early Muslim conquests in the mid-7th century East, or as roughly contemporary with the Sasanian Empire (224–651).
Wikipedia – Late Antiquity
Evidently, the original authors of the Roman narrative didn’t devise a series of rip-roaring Roman romps for West Africa because West Africa was a Carthaginian domain.
The existence of the Senegal River was known to the early Mediterranean civilizations.
It or some other river was called Bambotus by Pliny the Elder (possibly from Phoenician “behemoth” for hippopotamus) and Nias by Claudius Ptolemy.
It was visited by Hanno the Carthaginian around 450 BCE at his navigation from Carthage through the pillars of Herakles to Theon Ochema (Mount Cameroon) in the Gulf of Guinea.
There was trade from here to the Mediterranean World, until the destruction of Carthage and its west African trade net in 146 BCE.
Wikipedia – Senegal River
Court Historians [at some point] adjusted the preposterous “300 years out of fashion” Diocletian narrative to include the fictional creation of Libya Inferior in North Africa.
LIBYA, the Greek name for the northern part of Africa, with which alone Greek and Roman history are concerned.
It is mentioned as a land of great fertility in Homer (Odyssey, iv. 85), but no indication of its extent is given.
It did not originally include Egypt, which was considered part of Asia, and first assigned to Africa by Ptolemy, who made the isthmus of Suez and the Red Sea the boundary between the two continents.
The name Africa came into general use through the Romans.
In the early empire, North Africa (excluding Egypt) was divided into Mauretania, Numidia, Africa Propria and Cyrenaica.
The old name was reintroduced by Diocletian, by whom Cyrenaica (detached from Crete) was divided into Marmarica (Libya inferior) in the east, and Cyrenaica (Libya superior) in the west.
1911 Encyclopædia Britannica – Volume 16 – Libya
Diocletian‘s Tetrarchy reforms of 296 altered Cyrenaica‘s administrative structure. It was split into two provinces:
Libya Superior or Libya Pentapolis, comprising the above-mentioned Pentapolis, with Cyrene as capital,
Libya Inferior or Libya sicca, the Marmarica, which had by then gained a significant city, the port Paraetonium.
Wikipedia – Cyrenaica
Diocletian was a Roman emperor from 284 to 305.
Wikipedia – Diocletian
Diocletian (ca. 284-305[=1-14=700-714]) is seen as the most radical of all the Late Antiquity repeaters of everything 300 years out of fashion.
Rome’s Imperial Stratigraphy Belongs To The 8th-10th Century Period
Q-Mag – Gunnar Heinsohn – 22 June 2014
These academic issues coupled with the gradualist mindset make it extremely difficult / impossible [delete as appropriate] for mainstream researchers to reconcile Ptolemy’s map of West Africa with modern maps without making some astonishing alignments.
The Niger River is the principal river of West Africa, extending about 4,180 km (2,600 mi). Its drainage basin is 2,117,700 km2 (817,600 sq mi) in area. Its source is in the Guinea Highlands in southeastern Guinea. It runs in a crescent through Mali, Niger, on the border with Benin and then through Nigeria, discharging through a massive delta, known as the Niger Delta (or the Oil Rivers), into the Gulf of Guinea in the Atlantic Ocean.
Wikipedia – Niger River
Christian Marx suggests the Fortunate Isles align with the Canary Islands.
The localisation of Ptolemy’s places is based on distances derived from Ptolemy’s coordinates and partly on further information by ancient authors.
Through it previous identifications are confirmed and new identifications are found.
It shows that the Fortunate Islands correspond to several eastern islands of the Canary Islands.
The western coast of Africa in Ptolemy’s Geography and the location of his prime meridian – Christian Marx – Hist. Geo Space Sci., 7, 27–52 – 2016
An alternate allocation drops the two suspiciously small islands and adds Concepcion Bank at the start and La Gomera at the end of the reconciliation.
Malaga Bay – Cape Bojador and The Fortunate Islands
The Cape Verde Islands are also prime candidates for the Fortunate Isles.
Cape Verde, officially the Republic of Cabo Verde, is an island country in the central Atlantic Ocean.
The ten volcanic islands in its archipelago have a combined land area of about 4,033 square kilometres (1,557 sq mi).
The islands lie about 600 to 850 kilometres (320 to 460 nautical miles) west of Cap-Vert which gave its name to the islands.
On this cape – the westernmost point of continental Africa – lies Dakar, the capital of Senegal. Cape Verde forms part of the Macaronesia ecoregion, along with the Azores, Canary Islands, Madeira, and the Savage Isles.
Wikipedia – Cape Verde
Santiago is the largest island of Cape Verde, its most important agricultural centre and home to half the nation’s population.
It was the first of the islands to be settled: the town of Ribeira Grande (now Cidade Velha) was founded in 1462. Santiago is home to the nation’s capital city of Praia.
Wikipedia – Santiago, Cape Verde
Modern Earth Scientists will find matching the Fortunate Isles with the Cape Verde Islands just as mind boggling as the Canary Islands.
However, the Cape Verde Islands are far more plausible candidates because the latitude ranges of the two island chains [do at least] overlap.
Wikipedia – List of islands of Cape Verde
The Senegal Swing aligns Dakar with the Fortunate Isles and the Cape Verde Islands.
Malaga Bay – The Senegal Swing
Boa Vista is a desert-like island that belongs to the Cape Verde Islands.
At 631.1 km2 (243.7 sq mi), it is the third largest island of the Cape Verde archipelago.
The island of Boa Vista is closer to the African continent than all the other islands in Cape Verde, being the easternmost island of all.
The distance between Boa Vista and Senegal is only 450 km.
Wikipedia – Boa Vista, Cape Verde
Fogo is an island in the Sotavento group of Cape Verde. … It reaches the highest altitude of all the islands in Cape Verde, rising to 2,829 metres (9,281 feet) above sea level at the summit of its active volcano, Pico do Fogo.
Wikipedia – Fogo, Cape Verde
Dakar is the capital and largest city of Senegal.
The area around Dakar was settled in the 15th century.
The Portuguese established a presence on the island of Gorée off the coast of Cap-Vert and used it as a base for the Atlantic slave trade.
Wikipedia – Dakar
The position of Dakar on Ptolemy’s map aligns with known features.
The Senegal River is a 1,086 km (675 mi) long river in West Africa that forms the border between Senegal and Mauritania.
Wikipedia – Senegal River
The Gambia River is a major river in West Africa, running 1,120 kilometres (700 mi) from the Fouta Djallon plateau in north Guinea westward through Senegal and The Gambia to the Atlantic Ocean at the city of Banjul. It is navigable for about half that length.
Wikipedia – Gambia River
Fouta Djallon is a highland region in the center of Guinea, roughly corresponding with Middle Guinea, in West Africa.
Wikipedia – Fouta Djallon
The two unidentified islands to the North of the Fortunate Islands are good candidates for matching with the highest Canary Islands.
Wikipedia – Canary Islands
Mount Teide is a volcano on Tenerife in the Canary Islands, Spain. Its summit (at 3,718 m (12,198 ft)) is the highest point in Spain and the highest point above sea level in the islands of the Atlantic.
Wikipedia – Teide
Roque de los Muchachos (English: “Rock of the Boys”) is a rocky mound at the highest point on the island of La Palma in the Canary Islands, Spain. The rocks are found at an elevation of 2,423 m above sea level, not far from the Observatorio del Roque de los Muchachos, where some of the world’s largest telescopes are situated; the altitude and the dryness of the climate here give rise to excellent observing conditions.
Wikipedia – Roque de los Muchachos
Whether modern Earth Scientists can believe / accept / understand [delete as appropriate] that the rest of the Canary Islands emerged from beneath the waves [or broke free from Africa as trailing edge artefacts] in the Current Era is another mind boggling question altogether.
But, as always:
Evaluate the evidence and draw your own conclusions.