The bull is a symbol of strength and virility.
Unhappily, but almost inevitably, over-culture led to a gradual falling-off from the old virility.
Unlike the nobles, commoners did not use the size of their codpiece as an indication of status or virility.
As an aphrodisiac it enhances libido and can help re-activate sexual virility.
Ucko points out that in some groups the youth wear penis sheaths at a time in their lives when virility is alluring and the elders are freed from the responsibility of this signal.