Fable
The gatekeeper and the rulemaker
After the northern frontier new city was built, two important posts were established. Captain Du guarded the city gate, managing entry and exit inspections—preventing assassins, checking for weapons, and verifying travel permits, so trouble from outside the city could not slip in. Lord Cao sat at the government office gate, managing the laws of the inner city—whether each blacksmith shop followed rules on fire use, whether taverns could operate late at night, and how neighborhood land disputes should be judged.
The two each managed their own area, keeping to their own side of the river, and things were peaceful for two years. Captain Du had checked fake travel permits at the city gate and caught spies posing as merchants. Magistrate Cao had judged cases of taverns disturbing the peace at the courthouse gate and fined a blacksmith for sparks splashing a neighbor. The city's people felt these two had guarded the city as solidly as iron.
In the spring of the third year, someone poisoned the well in the city center, and more than forty people fell ill within three days. After half a month of investigation, the poisoner was caught—a traveling acrobat from elsewhere. Captain Du's soldiers had checked him at the city gate; at the time his bundle contained only colored balls and brass rings, and his travel permit was genuine, so the soldiers let him in.
The matter blew up, and the old city lord summoned both men to the hall. Captain Du spoke first: "My duty is to guard the city gate. On the day he entered the city, he had no hidden knife at his waist, no weapon in his bundle, and his travel permit had been checked. I can't just block someone outside the city because he looks suspicious." Lord Cao replied: "I manage the rules of the inner city. Before he poisoned anyone, he had not violated a single city rule. No one reported him, no one filed a complaint—how could I have known in advance what he was going to do?"
After hearing this, the old city lord spread out a new city defense map. At the city gate, in addition to checking weapons and travel permits, one more question was added—"What do you plan to do in the city?" Those who could answer were let through; those who could not were taken back to the guard office for registration and given a slip of paper listing pending matters. On every street in the city, a block chief was appointed, specifically responsible for the entry, exit and movements of strangers on his own street, and reporting anomalies directly to Lord Cao.
The most critical change was not at the city gate, nor at the government office, but between the two desks: Captain Du's inspection records had to be copied daily and sent to Lord Cao's desk. The headmen's record books under Lord Cao also had to be copied weekly and returned to Captain Du. If Lord Cao discovered that a registered outsider had not appeared in any street's records for three days, he was to notify the gate guard immediately—the person might be hiding.
The new rules had been pushed for half a year, and no more poisoning cases had occurred in the city. A neighboring city's defending general came to ask for advice. The old city lord said only one thing: there must be no gap between the rules and the city gate—when the assassin is outside, it is Captain Du's business; after he slips in, it is Lord Cao's business, but the assassin will not tell you whether he currently counts as inside or outside the gate.