In Russian it isn't exactly unnatural (certainly nothing which could be compared to the Latin poetry, where they often utilized an almost random, highly unprojective word order), but the word orders which would be otherwise emphatic aren't actually percieved as such in poetry.However, in BCS which is free word order, the poetic word order is not unnatural. But usually, if a language has a sentence structure that sounds weird, it is usually written of as poetic in linguistics.
Там врагу заслон поставлен прочный ©In Russian it isn't exactly unnatural (certainly nothing which could be compared to the Latin poetry, where they often utilized an almost random, highly unprojective word order), but the word orders which would be otherwise emphatic aren't actually percieved as such in poetry.
Well, in practice you can get the same number of syllabes, since French counts 6 syllabes to the last stress, and the same for Italian and Spanish. So, if you scan this verse following Spanish rules, you get 14:It is also interesting to know some of the differences among languages when counting those meters in poetry.
For instance, in the Romance languages, the Alexandrine verse in Catalan, French and Occitan is made of 12 syllables divided by a caesura (6+6), while in Italian and Spanish it's got 14 syllabales (7+7). This is mainly due to differences in word length and this affects the way of counting syllables in verses.
To be pedantic, we can say that divergence from usual language has an "indexical" function (to point to the fact that we are uttering poetry) and an "iconic" function (to build well-sounding utterances).The short answer is to make the words fit the meter.
The longer answer is that poetry is an art form which has its own rules. though they may differ according to time and place. In poetry every word can be considered a piece of a mosaic which is chosen carefully and put in the right place according to the effect you want to achieve. If poetry wanders too far from syntax though it risks being obscure - which is only fine if you want to be obscure.