Cats In Cyprus
 

I was told this story was told me today by my friend, that who recently came back from a vacation that he spent in Cyprus, so I cannot be sure/ (I am unsure) of the authenticity of the following:)
This summer he and his family travelled to Cyprus. They were wondered surprised of how much many cats there were! Cats were everywhere! On historical reasons, cats are not kept in houses because every cat is recognized as having public ownership. There is even a cat's monastery!
In the early 4th century, there was a drought in Cyprus which resulted to in the presence of a huge number of snakes. And Therefore, people began to leave their houses, so the island became almost was deserted. Saint Helena decided to create a monastery in Cyprus and sent there thousands of cats from Egypt and Asia Minor to deal with the snakes. Cats perfectly did the task and after several years, the island was cleared of the snakes. Since that time, cats became the most revered animals in Cyprus.

Quite an interesting legend! I've never heard of it before. I noticed that in Croatia there are a lot of cats as well. 
As for the corrections, here are some further explanations:

1. Correct is 'to be sure of' or 'to be sure about' (in your text : ...'be sure of the authenticity...' 

2. The use of 'much' and 'many':  
    "Much" is used for uncountable nouns (singular): How much water did you buy? We don't have much time to lose. How much money do you have?
     "Many" is used for countable nouns (plural): How many cats did you see? Were there many kids at the museum?

Cats In Cyprus

This story was told to me today by my friend that who recently came back from the vacation[holiday] that he spent in Cyprus. So I cannot ensure the authenticity of the following:)
This summer he and his family travelled to Cyprus. They were wondered how much many cats are there! Cats were everywhere! On For historical reasons, cats are not kept in houses because every cat is recognized[recognised] as a public ownership. There is even a cats monastery!
In the early 4th century there was a drought in Cyprus which resulted to a huge number of snakes. And People begin to leave their houses, the island was almost was deserted. Saint Helena decided to create a monastery in Cyprus and sent there thousand of cats from Egypt and Asia Minor to deal with the snakes. The cats perfectly did the task perfectly and after several years the island was cleared of the snakes. Since that time cats became the most revered animals in Cyprus.

I've not heard this story before, but I have been places where cats do seem to dominate!

People who share their life with cats usually consider that it's the cat that 'owns' the human...

The words in [] are the English version of the American word you used.

I've tried to make minimal chnges to your words, Natalia.

Den.