"I know these cities."

Translation: Я знаю эти города.

[JewishPolyglot]

Interesting... Why is the plural of город города instead of городи or something like that?

[AntoineFab]

I got it wrong as well :), it's just an irregular form, the most common ones are given on this page : http://www.russianforeveryone.com/Rufe/Lessons/Course1/Grammar/GramUnit2/GramUnit2_2.htm

[Jeffrey855877]

Note that the linked article refers to a stressed ending. That changes the pronunciation of города:

Genitive (stressed 1st syllable): "Gó-ra-da"

Nominative/accuative plural (stressed ending): "Ga-ra-Dá"

The change is due to the difference between stressed and unstressed "o" in Russian.

[JewishPolyglot]

Спасибо!

[lgularte]

Can we leave out "Я"?

[Jeffrey855877]

No. Russian almost always requires the subject pronoun to be present. I know there are rare instances where it's not used, but I can't think of any right now.

[Balti2Ukra]

In spoken Russian, from what ive heard from talking to people, its very common to speak without using pronouns. Понимаешь/понимаете? Is a common instance where its not present.

[guido506552]

This sentence is not at its place, it seems (город never presented in plural, nor plural accusative)

[jQuasebarth]

Does "знаю" require the accusative case?

[elsantodel90]

Yes, but for plural inanimate nouns it is just the same as the nominative. Note that "города" here is not the singular accusative of "город", but the plural accusative (which is the same as the nominative, and it is an irregular form).