Installer getting 'Unable to find a matching SQL Class'

I’m following to install drupal on FreeBSD 11.1 with mariadb55, php56, py27 and apache24

drush dl drupal --drupal-project-rename=sitename
cd sitename
drush site-install standard --db-url='mysql://user:[email protected]/sitename' --site-name=sitename

and I get:

exception 'DrushSqlSqlException' with message 'Unable to find a matching SQL Class. Drush cannot   [error]
find your database connection details.' in
Stack trace:

Not an inspiring start 😉  I was able to connect to the database with the given credentials…