Thy borders are in the midst of the seas, thy builders have perfected thy beauty.

And situate in the heart of the sea. Thy neighbours, that built thee, have perfected thy beauty:

In the heart of the seas are thy borders, Thy builders have perfected thy beauty.

Your borders are in the middle of the seas, your builders have perfected your beauty.

Your builders have made your outlines in the heart of the seas, they have made you completely beautiful.

for I have been positioned at the heart of the sea!' Your neighbors, who built you, have filled up your beauty.

Thy builders have perfected thy beauty - Under the allegory of a beautiful ship, the prophet, here and in the following verses, paints the glory of this ancient city. Horace describes the commonwealth of Rome by the same allegory, and is as minute in his description, Carm. lib. 1. Od. xiv: -
O navis, referent in mare te novi
Fluctus? O quid agis? Fortiter occupa
Portum. Nonne video, ut
Nudum remigio latus,
Et malus celeri saucius Africo,
Antennaeque gemant? ac sine funibus
Vix durare carinae Possint imperiosius
Aequor! non tibi sunt integra lintea;
Non Di, quos iterum pressa votes malo:
Quamvis Pontica pinus,
Sylvae filia nobilis,
Jactes et genus, et nomen inutile
Nil pictis timidus navita puppibus
Fidit. Tu, nisi, ventis
Debes ludibrium, cave.
Unhappy vessel, shall the waves again
Tumultuous bear thee to the faithless main?
What, would thy madness thus with storms to sport?
Cast firm your anchor in the friendly port.
Behold thy naked decks, the wounded mast,
And sail-yards groan beneath the southern blast.
Nor, without ropes, thy keel can longer brave
The rushing fury of the imperious wave:
Torn are thy sails; thy guardian gods are lost,
Whom you might call, in future tempests tost.
What, though majestic in your pride you stood,
A noble daughter of the Pontic wood,
You now may vainly boast an empty name,
Of birth conspicuous in the rolls of fame.
The mariner, when storms around him rise,
No longer on a painted stern relies.
Ah! yet take heed, lest these new tempests sweep,
In sportive rage, thy glories to the deep.
Francis.
I give this as a striking parallel to many passages in this chapter.

Thy borders are in the midst of the seas, Fixed by the Lord himself, and which could never be removed. Tyre stood about half a mile from the continent, surrounded with the waters of the sea, till it was made a peninsula by Alexander:
thy builders have perfected thy beauty. The Sidonians were the first builders of the city, as Justin (q) says; who began and carried on the building of it to the utmost of their knowledge and skill; and which was afterwards perfected by other builders, who made it the most beautiful city in all those parts; unless this is to be understood of her shipbuilders, who brought the art of building ships in her to such a perfection, as made her famous throughout the world; since they are immediately spoken of without any other antecedent.
(q) Ex Trago, l. 18. c. 3.

Tyre, in consonance with her seagirt position, separated by a strait of half a mile from the mainland, is described as a ship built of the best material, and manned with the best mariners and skilful pilots, but at last wrecked in tempestuous seas (Ezekiel 27:26).