Homemade spikes that could cause serious injuries have been found on a NSW Central Coast running trail.
A jogger discovered the crude devices - consisting of nails protruding from wine corks - on Alexanders Trail in Lake Macquarie State Conservation Park on Monday morning.
Police say the objects are similar to "historic weapons known as caltrops" that were used as a weapon in wars by the ancient Greeks and Romans to pierce the feet of unsuspecting enemies.
The spikes were uncovered after the runner noticed a pile of leaves in the middle of the track with the devices hidden underneath.
He found another two piles further along the track.