How to interleave the lines of two text files in Linux?

Question

What's the easiest/quickest way to interleave the lines of two (or more) text files? Example:

File 1:

line1.1
line1.2
line1.3

File 2:

line2.1
line2.2
line2.3

Interleaved:

line1.1
line2.1
line1.2
line2.2
line1.3
line2.3

Sure it's easy to write a little Perl script that opens them both and does the task. But I was wondering if it's possible to get away with fewer code, maybe a one-liner using Unix tools?

Answer 1

paste -d '\n' file1 file2

Answer 2

cat file1 file2 |sort -t. -k 2.1

Here its specified that the separater is "." and that we are sorting on the first character of the second field.