The relics can be obtained completing the quest "Adventure" (bottom right buton). To obtain parts of map you must defeat Robber Baron Castles.  You must obtain all the parts of a map to access to the quest, which you then must defeat castles, and repair bridges to complete the "Adventure" and obtain the relic.

Depending the level of the castle you have more or less possibilities of getting a part of the map. Each map have a specific number of parts, having more the later relics. 

These are the relics that you can obtain in order of apparition:

            Name                     PO              Size

• Ancient relic:             14               3x3

• King Pig                     18               3x3

• War Banner               22               3x3

• The Clever Wives      26               3x3

• Flat Earth                   52              4x4

• Brave Farmer 35      35               3x3

• Robber Captain         40               3x3

• Honorable Warrior    41              3x3

EverWinter Glacier adventure map

• True friends              :42