New timeline when starting with a restored data dir

[Yuri Kanivetsky <yuri.kanivetsky@xxxxxxxxx>]

Hi,

I'm trying to set up Barman, and I've noticed that PostgreSQL 10
creates a new timeline when starting with a restored data dir.
Particularly, when WAL files are delivered via restore_command. When
WAL files are copied to pg_wal dir, no new timeline is created. Is it
to be expected? Can you explain?

I decided to ask here first, since you might know better how
PostgreSQL operates.

Thanks in advance.