Why are the Ancient Greek and Roman mythologies so similar? ?

As the Romans conquered different cultures, they assimilated their gods in order to not upset those they had conquered.

Why are all the stories about divine beings so much the same?  Like the story about Jesus there are many religions about a guy born to a virgin mother, a guy who walked on water, a guy who rose from the dead.  All ancient belief systems have similar threads.

Great question.  Their languages are not even close.  Greek is Indo Hellenic and Italian is Proto European Italic.

The Ancient Greek Empire existed first.  They brought geometry into existence.  Pythagorus was Greek. Aristotle was Greek. They brought about the first democracy.  So all people had a vote(all men anyways) No longer was there to be a King. They existed for quite awhile and they developed their Gods with complete descriptions in appearance , powers & temperaments. Their head God was Zeus, Zeus was jealous of humans because they could love and Gods can't so Zeus transformed into a mortal and had sex and Hacales was born to a mortal woman.

Not a god but not a man - he was a demi-God.

The Roman Empire defeated the Greek Empire so Rome was now the dominant force.  As much of its citizenry was Greeks, Rome DID assimilate the Greek religion into its own culture (keeping the descriptions of the Gods but gave them "Roman" names.  Zeus became Jupiter, Hacales became Hercules, Aphrodite became Venus, Apollo became Mercury(the dude with the winged feet).  Rome was a militaristic civilization, more interested in dominating other regions rather than politics or the arts or mathematics or philosophy.

Many Greeks were employed by the Romans to help them build their city structures and navy.  As the god description remained the same, to the Greeks, they shrug their shoulders when the name changed. They knew who they were talking about because they used the Greek descriptions of the Gods.   So when you look for certain gods certain name are used Hercules and Zeus(Rome & Greek intermingled) Poseidon was the Greek god of the Ocean (Rome's name is Neptune)(Pluto is Roman God of Underworld-Hades is the Greek name for the same place) To the Greeks hell was a place of "nothingness" darkness" "non existence"  >No fire, no brimstone, no demons(all Christian beliefs)

When you watch the old time movies you will find that there is a flip flop of the names.  I guess for the movies one sounds better than the other.

You have heard the term "Kraken".  That was never used by the Greeks they had the Cetus (Seetus)(a  wormlike monster.)

Though movie makers have used the name Kraken(because it sounded kool)over the name Cetus and it is liberties in artistic interpretation <the Kraken comes from Scandinavia( so something of Viking Lore) with was like a huge octopus that would take down the wooden ships> so Pirates of the Caribbean would have got the Kraken

Rome never spoke of an equal to the Cetus...as they were not a naval force like the Greeks were.

It's the progression of Gods to coincide with the progression of man.

The Greeks got democracy aka philosophy and spirituality from KEMET.

The Romans developed religion from mythology with Christ as thee religion from Greece.  And Ind so forth all the way up today.

But only Kemet is denied it's rightful place in the annuals of great KINGDOMS....👁️

There's a variety of reasons for this as most myths and religions derive off of preexisting cultures. Even the Greek gods have counterparts in ancient Egypt.

Greece and Rome were not too far from eachother in terms of location, but because of the Adriatic Sea, Greece is isolated enough for its language to have evolved separately. Language and Mythology don't evolve at the same pace. Look at the Bible, despite being written, translated and retranslated dozens of times, the story whether in English, Old English, Polish or Italian, the themes and stories are pretty close, despite the errors of translations.

It's not so much that Rome assimilated the myths of Greece upon conquering it; it's more so that Rome adopted the myths before its rise to power because Greece was the "World Power" before Rome. Greece came to global (or what was Global at that time) prominence by defeating the Persisn Empire, which was determined to take over the world. It's far more likely that Rome accepted these beliefs during its early development as an evolving Empire, not after.

Greece was a World Power for 2 and a half centuries before Rome took over. Although Geeece didn't focus on conquest its sphere of influence could've easily reached a young Rome. 200 years isn't long enough for myths to change form. It's probably due to the Greek's ideologies on philosophy and learning, if not a far more ancient tradition, being passed on that led to this adoption.

Jupiter and Zeus are the same entity. As are Mars and Aries, etc. The names are only changed due to language differences.

Greek Mythology is fully different from Roman Mythology

Because the Romans conquered the Greeks, which entitled them to steal the Greek religion and make it their own.  That's literally why.

It wasn't personal, in fact religions have been doing that for thousands of years.  Some emperor / warlord / king / pope / whatever would hear a series of stories from another culture, say "well that's pretty cool", and then assimilate that cool stuff into their own religious belief.  All the religions do it.

Proto-Indo-European mythology is the body of myths and deities associated with the Proto-Indo-Europeans, the hypothetical speakers of the reconstructed Proto-Indo-European language. Although the mythological motifs are not directly attested – since Proto-Indo-European speakers lived in prehistoric societies – scholars of comparative mythology have reconstructed details from inherited similarities found among Indo-European languages, based on the assumption that parts of the Proto-Indo-Europeans' original belief systems survived in the daughter traditions. The Proto-Indo-European pantheon includes a number of securely reconstructed deities such as *Dyḗws Ph₂tḗr, the daylight-sky god; his consort *Dʰéǵʰōm, the earth mother; his daughter *H₂éwsōs, the dawn goddess; his sons the Divine Twins; and *Seh₂ul, a solar goddess.