bash - combine 2 files

hello
i have 2 files .. file1 and file2, with text
how can i make a third file (file3) that contains on the first line, the first from file1, on the second, the first from file2, on the third, the second from file 1, on the fourth, the second from file 2
so, basically, combine .. one line from file1, one from file2 .. etc in file 3

thanx