A series of earthworks running the length of the Welsh border from near the mouth of the Wye to near the mouth of the Dee, built or repaired by Offa (king of Mercia, 757–96) to mark the boundary established by his wars with the Welsh.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。