Del. Code tit. 17, § 509

All public roads, causeways and bridges laid out as such, or made by lawful authority, or which have been used as such and maintained at the public charge for 20 years or more are declared to be common highways. The usage by the public for 20 years or more of any road shall not cause the road to become a common highway or public road unless the same has been maintained at the public charge for 20 years or more.