Zürich was an independent (reichsfrei) city orcity-state from 1218 to 1798. The town wasfortified with acity wall from the 13th to the 17th century, and with more elaborateramparts constructed in the 17th to 18th century and mostly demolished in the 1830s to 1870s.

There had been a first city wall dating to the 11th or 12th century. The existence of such an early wall had been suggested, but the mainstream view assumed that the town had been unfortified – the remains of the Roman castle at theVicusTuricum, and a so-calledKaiserpfalz onLindenhof hill excepted – before the 13th century, until the chance discovery of remnants of the first wall during the 1990s construction work at thecentral library respectively location of thePredigerkloster, the former Dominican abbey.

Following the extinction of the main line of theZähringer family in 1218, Zürich became afree imperial city. Over the following decades, a city wall was constructed over a length of some 2,400 m.

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  1485 depiction of the 1444 siege of Zürich during theOld Zürich War (north is right)
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  1581 depiction of Zürich (north is left)
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  1904 map of Zürich in 1504
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  Schanzengraben,Enge quarter,Zürichsee andAlbis chain, as seen from the «zur Katz» ramparts (as of today the"old" Botanical Garden)
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  Remains of the medieval city walls in a basement ofZentralbibliothek Zürich respectively at the location of today'sPredigerkirche
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  TheRennweg gate in 1812
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  TheOetenbach bulwark (built 1532) just before its demolition in 1903
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  Bilgeri tower atNeumarkt
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  Brunnenturm (fountain tower) nearNiederdorf
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  Glentner tower atLimmatquai
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  Grimmenturm at Neumarkt
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  Hardturm next to theLimmat (Industriequartier)
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  Mülnerturm orSchwert house atWeinplatz (Rathausbrücke)
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  Steinhaus at Hirschengraben

The irrigated grave system of medieval Zürich, consisting of the internal (i.e. inside the town wall)Fröschengraben, the outerSihlgraben and the intermediate town wall was first mentioned in 1258 AD asniuwer graben (new moat); the presentSchanzengraben was still in construction around 1300. Over the decades, the time accumulating sludge was periodically dug out by day laborers or in forced labor to process. Due to its former military defensive use, the moat has a widely octagonalzig-zag form, and was completed as part of the Baroque fortifications of Zürich around 1642 AD, and theBollwerk zur Katz became the eastern gunnery bastion of the city fortification.

In the late Middle Ages, the presentSechseläutenplatz area was the location of the former military harbour of the city of Zürich respectively part of the so-calledStadelhoferbollwerk bastion on Zürichsee lakeshore. The former Stadelhofer bulwark also was built as part of the so-calledfourth city fortifications in 1643 AD. The bastion was built partly into the lake, and in 1673 the Stadelhofen ravelin was attached, and completely broken in 1837/38.^[1][2]

TheOetenbachbollwerk was a bastion of the fortifications, and was built under the supervision of Balthasar Keller in 1532. The stronghold replaced a wooden mounting in the garden of the Oetenbach convent and had to secure the western town wall and the gate at the Limmat. In 1642 the bulwark was covered, and in 1764 the adjoiningWaisenhaus building provided as a storage room and economics building. In 1903 the bastion was broken as the last construction of the city's fortifications. Numerous finds came to light, including the grave stone ofUlrich I von Regensberg, which was misused as a loophole cornice of the bulwark.^[3]

From 1558 to 1562 the roundAuf Dorf bastion with battlements was built at the site of the presentBellevueplatz at the junction ofLimmatquai andRämistrasse. Structurally, it was connected to theLangenöhrlisturm of the city fortification, and originally surrounded almost entirely by the water ofZürichsee respectivelyLimmat. The bulwark comprised casemates with loopholes and a platform for the artillery to defend against attackers on the lake, and to complete the oppositeBauschänzli bastion respectively the medievalGrendeltor. The remains were discovered on occasion of road works in March 2015.^[4]

From 1642, an impressive set of ramparts was built based on plans by Hans Georg Werdmüller and Johann Ardüser, at an immense cost and completed only in the second half of the 18th century. The ramparts included fifteen bastions, one of them built inside the Limmat (theBauschänzli, location of the formerRavelin Kratz).

The ramparts were mostly destroyed in 1834, but parts of the walls and the western moat remain visible.

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  1793 map of Zürich (north is left), the so-calledMüllerplan
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  The moat (Schanzengraben) and the remains of theBollwerk zur Katz (Old Botanical Garden), next toSelnau station.
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  18th century sketch of the old and new walls on either side ofParadeplatz (at the time known asNeuer Markt).
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  Stadelhoferbastion and formerwar harbour at, as of today,Sechseläutenplatz andStadelhoferplatz

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