六街三市 Six Streets And Three Markets
長老策馬，須臾到門。下馬過橋，進門觀看。只見六街三市，貨殖通財；又見衣冠隆盛，人物豪華。长老策马，须臾到门。下马过桥，进门观看。只见六街三市，货殖通财；又见衣冠隆盛，人物豪华。
逐句解 Line by line
The elder put his horse forward, and in a moment they were at the gate.
策馬 is urging a horse on with the whip, and it answers 勒住馬 four passages back, where he reined the same horse in to ask what the place was. 長老 zhǎng lǎo takes zhǎng, the elder, not the cháng of length.
They dismounted, crossed the bridge, went in at the gate and looked about them.
Four verbs in four characters, no subject named and nothing joining them: this is how the novel moves a party through a gate when nothing is at stake in the crossing.
They saw six avenues and three markets, goods multiplying and money moving freely;
六街三市, six streets and three markets, is a set phrase for a great city's full commercial layout rather than a count of anything. 貨殖 huò zhí is goods multiplying — the term the 《史記》 uses for its chapter on merchants.
and they saw caps and gowns in their splendour, and the people magnificent.
衣冠 yī guān is cap and gown, the dress that marks office and standing, and 冠 keeps the level-tone noun rather than the falling-tone verb, to cap. This couplet is the last of the good news.
The entry takes twenty-four characters and every one of them is favourable. Streets, markets, goods, money, dress, people: the prose is confirming from the inside everything the rhapsody claimed from outside the wall, and doing it in the flat voice of a report rather than in verse.
That is the setup. The novel has spent a poem and an argument establishing that this is a great capital, and has now walked the reader through the gate to see that it really is one. The next sentence undoes all of it.