An American bald eagle holding three crossed arrows with its wings spread horizontally and a thirteen-piece Argent and Gules shield with an Azure chief on its breast. An arc of thirteen stars with alternating beams can be seen above the eagle. 

The Depiction.

A wreath of laurel and olives to the left and right of the eagle, respectively. The words 'DEPARTMENT OF DEFENSE' and 'UNITED STATES OF AMERICA' are inscribed on an encircling ring, respectively. The background, proper eagle, wreath, and yellow/gold arrows, stars, and rays will all be depicted in the seal's color illustrations. With yellow/gold margins and white text, the encircling band will be dark blue.

A manipulus, which is a bunch of straw attached to the end of a spear and somewhat resembling a fasces, was the earliest military emblem we are aware of being employed by the Romans. It possibly served as a visual cue for a 'maniple,' or a small group of organized men.

Some Historical background of the use of eagle as an emblem in the army.
 

The battlefield unit emblems used by the Romans served a very useful function. They would have served as the unit's focal point and visual identity, around which they would have based their fighting formation and which would have aided in the execution of maneuvers. However, as the military progressed and new leaders emerged the symbol of eagle  became rigid which represented the strength of the army.

The Eagle, Globe, and Anchor, which has stood in for the title every Marine has earned since 1868, is the best representation of the mission we serve. 

The eagle stands for the proud Nation that we protect. With our coastlines in view and the entire planet within reach of its outstretched wings, it waits at the ready. The globe symbolises our presence, influence, and reputation as a force that fights and prevails on behalf of the advancement of our country's citizens. 

The Marine Corps' naval history and its capacity to reach any battleground along any shoreline worldwide are both referenced by the anchor. The eagle, globe, and anchor represent our shared resolve to uphold and defend our nation's ideals.

I hope you liked my answer.