Periodic sentence

A periodic sentence is a stylistic device employed at the sentence level, described as one that is not complete grammatically or semantically before the final clause or phrase.
Characteristics.
The periodic sentence emphasizes its main idea by placing it at the end, following all the subordinate clauses and other modifiers that support the principal idea. The sentence unfolds gradually, so that the thought contained in the subject/verb group only emerges at the sentence's conclusion. Obviously artificial, it is used mostly in what in oratory is called the grand style.
It is the opposite of the loose sentence, also continuous or running style, where the subject and verb are introduced at the beginning of the sentence. Periodic sentences often rely on hypotaxis, whereas running sentences are typified by parataxis.
Cicero is generally considered to be the master of the periodic sentence.
Decline.
In English literature, the decline of the periodic sentence's popularity goes hand in hand with the development toward a less formal style, which some authors date to the beginning of the Romantic period, specifically the 1798 publication of the "Lyrical Ballads", and the prevalence in twentieth-century literature of spoken language over written language. In American literature, scholars note the explicit rejection by Henry David Thoreau of the formal style of his time, of which the periodic sentence was characteristic; in his journal, Thoreau criticized those sentences as the "weak and flowing periods of the politician and scholar."
Rhetorical and literary usage.
According to William Harmon, the periodic sentence is used "to arouse interest and curiosity, to hold an idea in suspense before its final revelation." In the words of William Minto, "the effect...is to keep the mind in a state of uniform or increasing tension until the "dénouement"." 
In his "Handbook to Literature", Harmon offers an early example in American literature found in Longfellow’s "Snowflakes":
Starting with a succession of parallel adverbial phrases ("Out of the bosom," "Out of the cloud-folds," "Over the woodlands," "Over the harvest-fields"), each followed by parallel modification ("of the air," "of her garment shaken," "brown and bare," "forsaken"), the sentence is left grammatically incomplete until the subject/verb group "Descends the snow". Other American examples cited include the opening lines of William Cullen Bryant's "A Forest Hymn" and lines 9-16 of his "Thanatopsis". A particularly long example is the opening stanza (lines 1-22) of Walt Whitman's "Out of the Cradle Endlessly Rocking."
A "now-famous periodic sentence" occurs in Nikolai Gogol's short story "The Overcoat":