The altar of Zeus on Mount Ainos in Kefalonia was connected to a nearby islet which is located in front of the Southern coast of the island. This islet is aptly called Dionisi (Διονήσι), meaning “island of Zeus” (Dias=Zeus, Nisi=Island).
On that small island, apparently, in antiquity there was a temple dedicated to Zeus which was built in order to face a bigger altar with the same name on top of Ainos mountain.
“Apparently” because it’s not entirely clear. Professor Niki Efthymiatou-Katsouni wrote:
Today there’s a chapel dedicated to the Virgin Mary Vlaherena and before that there was a monastery, which collapsed during the 1953 earthquakes. After the earthquakes only the chapel was reconstructed. Marinatos (1962) mentions the following testimony of the traveller D. Ansted (1863), regarding two parallel sacrifices to Zeus: while the first was taking place on the peak Megas Soros of Aenos and upon seeing the smoke, the priests would make a second sacrifice on the islet. Partsch (1892) and Marinatos (1962) express doubts, because this is not inferred from recorded testimonies and there are no ancient traces on the islet. Tsitselis (1877) mentions “stones of dubious origin”. However, as mentioned by Marinatos (1962), the scholar B. Schmidt, who wrote in 1871 about the Life of the Modern Greek people, speaks of the remains of an ancient building under the chapel of the Virgin Mary and the monastery.
Therefore, there exist two testimonies that in the 19th century there were still traces of an ancient building on Zeus islet and that the memory of the performed sacrifices of the past had not worn off. The small size of the islet, its steep and inclined surface and the successive destructive earthquakes contributed so that the scarce building traces rolled and fell into the sea. Since the earthquake of 1867 the entire coastal strip of Cephalonia Island along the Gulf of Lourdas and opposite Zeus sustained great damage. We do not know if in 1871, when Schmidt made his publication, he had recent information on the islet, i.e. gathered shortly before or shortly after the 1867 earthquake. In this case, the remains of the buildings that he mentioned could have disappeared during that seismic activity. We add that before 1867, 61 earthquakes occurred in Cephalonia, four of which were particularly destructive. From 1867 until 1953, 32 other earthquakes occurred (Toumasatos 2007).
In any case, the ruins on the islet of Zeus either disappeared with the 1867 earthquake and Schmidt recorded the still fresh memory, or they remained there for some additional time, only to be finally wiped out by the subsequent earthquakes. If the double sacrifice is indeed a fact, then it constitutes a large and important worship at an ancient, Panhellenic sanctuary.
On his famous work about placenames and toponymes in the island, Tsitselis wrote about the Dias islet:
Dias: a small islet off the southwestern coast of Krane, on the right as one enters the bay, where today is a small monastery of the Theotokos. It is likely that there was an altar to Zeus there in the past, but we have no evidence of this except tradition, the surviving name, and some stone of dubious history, as they say, the ruins of the temple; otherwise it is not entirely improbable, since it lies below the Aenos, where, as is well known, there was a temple to Zeus. The people today have combined, so to speak, according to the phrase of Mr. Mavrogiannis; the two religions, calling the monastery there “The Virgin of Zeus”. The “Lady of Zeus”, in which phrase the inflection of the name is also kept accurate. The most elegant small church was painted by the priest Kantounis from Zakynthos, a renowned iconographer, who happened to be exiled there for some time.
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«Smoke on the altar of the summit and in the islet»
In «The Ionian Islands in the year 1863», David Thomas Ansted (1814-1880) wrote that when smoke was visible on top of Mount Ainos, another fire was built in the islet of Dias:
The view from this summit when everything is favourable must be exceedingly grand, as, except the Pindus range which is distant, there is nothing to intercept the view. All around is a rich panorama of All around is a rich islands: Zante at one’s feet in all its elegant beauty of form; Ithaca to the east; beyond it a silver strip of ocean, and then the gulf of Patras, which is seen in all its length to the bay of Lepanto, in the vicinity of Corinth. Athens is not much further in the same direction. A noble chain of snowy mountains shuts in this view towards the south east. Looking down in the direction of Argostoli a minute speck is seen in the water. On the island called Διος (Thios), that looks so small, was once a temple to the father of the gods, and when sacrifice was offered and the smoke was seen by the priests stationed at the altar on this summit, another sacrifice was here made, and the curling incense rising from this lofty point in the thin air was a sign, far and wide, of the completion of the offering. Here above remain the stones of the altar and the burnt bones of the bulls and the goats; there below, at a distance of several miles, the more solid and beautiful temple is gone-not one stone remains upon another, and there is nothing but the story, probable enough for that matter, to connect the two localities. The permanent construction, carefully built to last for ever, has vanished! the few rough stones heaped together for a temporary purpose remain. So it often will be in this world of ours.
“The ruins of an ancient building are also preserved”
The Cephalonian historian Kostis Ioannis Loverdos, in his book “Ιστορία της νήσου Κεφαλληνίας” (“History of Cephalonia island”), written in 1888, page 14, mentions that there were ruins of an ancient building, perhaps a sanctuary of Zeus, so it’s reasonable that the remnants were still there in 1888:
Worthy of note is the rock called Zeus, three miles from the bay of Agia Pelagia. The ascent to it is made by a staircase with many steps, and the ruins of an ancient building are also preserved, from which it is assumed that there was a sanctuary to Zeus there, so the rock bears the name to this day. Its perimeter is about half a mile and today there is a small monastery on it.
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“Communicating by smoke”
Communicating sacrifices were not rare in antiquity. Processions, with their strongly performative aspects, created communication between sacred spaces, by which means a ritual topography was constituted. In this case, it is believed that when priests and priestesses would begin the sacrifice at Olympia’s Zeus altar, the smoke rising to the sky would be seen from the top of Aenos Mt (1,623m altitude), a sacrifice would then take place there, and subsequently to the islet of Zeus, perceptible from Aenos with SW orientation. A little orthodox church was built (it is not yet officially dated) on the top of the islet probably by hermits, while in 1805 three hieromonks (priest-monk) would live and act there. During the 19th century, the Vlahernon monastery was built on the island of Dias.
The small church of Virgin Diotissa
At south of Kefalonia, just half a mile from the shores of Leivatho there is the islet “Zeus”. The small church of Panagia Vlacherna or “Virgin Diotissa” is located at the top of the rock. A narrow staircase carved into the rock leads believers to church to celebrate each year on July 2nd. Ruins of an ancient temple which was dedicated to Zeus are also located here. In the 19th century there was here a great monastery which was dedicated to Our Lady, but it was completely destroyed by the earthquake of 1953. During the turbulent period of British rule in Kefalonia, the island was used as a place of exile for dissidents. Every year on July 2nd, the small island is full of people. Small boats that depart from Pessada deliver the believers and the icon of the Virgin of the Monastery of the Crucified on the island, where the liturgy takes place.
The feast of Panagia Diotissa (the Virgin Mary of Dias) takes place on the islet of Zeus, located to the south of Kefalonia. At 7 am, the boat from the port of Pessada starts on the day of the feast and transfer people to the island. Here there are the treats such as traditional “riganada” and other delicacies, under the big tent that shades the courtyard near the church after the liturgy.
“A marine Meteora”
The famous Greek archaeologist Spyridon Marinatos called the Dias islet “a marine Meteora”:
South of Kefalonia, at a distance of half a nautical mile from the shores of Livathos, the rocky isle of Zeus rises. Sharp on all sides and imposing, it has been characterized by Professor Spyros (Spyridon) Marinatos as “Marine Meteora”. The name Zeus received it, because in antiquity there was an altar of god Zeus on the rocky island. It is said that sacrifices were made at the same time with the altar of Zeus, which was at the top of Mount Ainos, hence the name Anisios. The coordination was done with the view of smoke.
The islet of Dias (Dionisi), with the Panagia Diotissa chapel on top of it:
From Zeus to Aphrodite and to Virgin Mary
On the island in Antiquity there was an altar to Zeus, hence its name, and later a temple to his daughter Aphrodite. According to an old story of a local from Pessada, mentioned by the 19th century traveler Alexander Freiherr (Baron) von Warsberg (1836–1889) in his book “ITHAKA”, published in Wien in 1887, pp. 12 to 30 and in the chapter there “Zeus im exil” (Zeus in exile), the ancient cult was abolished by the action of the new Apostle in Pessade (“der neuen Apostel in Pessades” pp. 24 &25) and converted to Christian. [Source and Alternate source]
As is known according to old tradition, but also the latest research, by Heinz Warnecke and the five relevant international scientific conferences, the Apostle Paul was shipwrecked in 59 AD in Pessada, going to Rome and christianizing Kefalonia, remaining on the island for three months. Thus the ancient sanctuaries of the island were replaced with Christian ones and the temple of Aphrodite, the goddess of love and beauty of the Ancient Greeks was replaced with a temple and honors to the Virgin Mary, the divine beauty! The people named her Diotissa after the name of the island.