Helen, thy beauty is to me
Like those Nicean barks of yore
That gently, o'er a perfum'd sea,
The weary, way-worn wanderer bore
To his own native shore.
Direct allusion to  Samuel Taylor Coleridge’s   Youth and Age  where he says, 
 How lightly then it flashed along, Like those trim skiffs, unknown of yore. 
 Nicean barks refers to the moment that the victorious Greek ships sailed home after the Trojan War. As beautiful as this moment was, Helen is even more beautiful. The mention of Nicea is important to emphasize the majesty of victory as Nicea is named for the Greek goddess of victory  Nike  (yes the shoe company is named after this goddess) 
 
 Notice the use of the word  like , meaning that this is a simile. A simile that extends for many lines, like this one, is referred to as a Homeric simile or an epic simile.
To Helen