Járnborg

As defined by A Concise Dictionary of Old Icelandic (Geir Zoëga):

járnborg

f. ‘iron-castle’ (used of a ring of iron-clad ships).

Possible runic inscription in Younger Futhark:ᛁᛅᚱᚾᛒᚢᚱᚴ

Also available in related dictionaries:

This headword also appears in dictionaries of other languages closely related to Old Icelandic.

• Old Norse - Cleasby & Vigfusson Dictionary
• Old Norwegian - Johan Fritzner's Dictionary