Just under the western heights run the Autobahn A 3 and the Cologne-Frankfurt high-speed rail line (in the Idsteintunnel along the slope).

Idstein, which had its first documentary mention in 1102 as Etichenstein, was granted town and market rights in 1287 by King Rudolph of Habsburg.

One of the Counts, Adolf of Germany, was, as a compromise candidate, the Holy Roman Emperor from 1292 to 1298, later falling in battle against the anti-king Albrecht I of Habsburg.

The Nassau Counts' holdings were subdivided many times among heirs, with the parts being brought together again whenever a line died out.

[6] In 1721, Idstein passed to Nassau-Ottweiler, and in 1728 to Nassau-Usingen, thereby losing its status as a residence town, although it became the seat of the Nassau Archives and of an Oberamt.

[citation needed] The private Kalmenhof clinic in Idstein was drawn into the Nazi Euthanasia programme.

After the gassings at Hadamar came to an end in the face of public protests, especially from the churches, the Kalmenhof itself, in the course of Aktion Brandt, became a killing institute; patients here were murdered with poison injections.

(as of 31 December) The town's arms might be described thus: Azure a round castle wall embattled with two portcullises open, the wall enclosing two towers, the whole Or, with peaked roofs gules, between the portcullises an inescutcheon azure with a lion rampant Or armed and langued gules among six billets Or.

[13] Another important employer and factor in the economy is the Landeswohlfahrtsverband Hessen (Hesse State Welfare Federation) with its SPZ (paediatric centre) Kalmenhof, an institution aiding youths and people with handicaps.

For the manufacturer, it is, with its cupola, biomass power plant and natural bathing pond a demonstration project near Frankfurt Airport.

The ceiling in the main nave was thoroughly covered with large-scale oil paintings from the Dutch school of Rubens.

Several well known works by Rubens form the basis of scenes from the life of Christ on the walls and ceiling; for example The Wedding at Cana[14] on the south wall is largely based on Rubens's painting The Feast of Herod[15] which hangs today in the National Gallery of Scotland in Edinburgh.

The castle in the area stretching from the gateway arch building on the town side to the bridge over to the Schloss arose between 1497 and 1588.

With the remodelling done on the palace itself in the 17th century, this area also underwent far-reaching changes, partly losing its defensive functions, which, it is worth noting, were no longer up to date anyway.

(Building researchers see in it a rare time capsule, because in the 20th century, almost nothing was changed beyond the last work in 1963, which entailed nothing more than some new plastering outside and small touch-ups with cement inside).

On the way out of the square towards the Unionskirche, is the richly adorned Killingerhaus built in 1527, which has served as a museum and tourism office since 1987.

According to one story, the building was originally built in Strasbourg, and when the owner moved to Idstein, he brought the house with him.

The rest of the old downtown core is also characterized by its many timber-frame houses and estate complexes from the 16th and 17th centuries, some of which have been lavishly renovated.

After they died out, ownership passed to the family von Calm between 1768 and 1776, giving the property on which it stands its current name, Kalmenhof.

As a last witness to the former leather industry, the Gerberhaus ("Tanners' House") stands at Löherplatz below the Unionskirche; it is the former storage shed on the Wörsbach.

As the former neogothic Catholic parish church St. Magdalena was too small for a growing population after World War II, a new church St. Martin was built instead, designed by the architect Johannes Krahn, resembling a Roman basilica with open sandstone walls and a band of windows below the ceiling, consecrated in 1964.

The municipal area was crossed by the Limes Germanicus, a line of frontier forts begun in AD 86 by the Romans which stretched from near Bonn on the Rhine to near Regensburg on the Danube.

Within the limits of neighbouring Taunusstein is likewise found such a replica near Orlen, right beside the remains of the castrum Zugmantel.

When, towards the end of the war, it was no longer possible to transfer people who had died in the hospital to their hometowns, they were buried in the Idstein cemetery.

On three days, during the first weekend in the Hesse summer holidays, up to 75 different jazz groups on a dozen stages play from Friday evening to Sunday live in an open-air concert.

The Unionskirche is the location for choral concerts of the Idsteiner Kantorei conducted by Carsten Koch twice a year, such as Orff's Carmina Burana and Bach's Weihnachtsoratorium in 2009.

For the annual European Heritage Days the "Nassauische Kammerphilharmonie" has performed a Sinfoniekonzert on the occasion of the Tag des offenen Denkmals, including a series of Beethoven's symphonies.

In the church St. Martin an annual choral concert is performed by the combined choirs Chor St. Martin and the chamber choir Martinis, conducted by Franz Fink, such as Bach's St Matthew Passion in 1998 with Elisabeth Scholl, Andreas Scholl and Max van Egmond and again in 2009 with Andreas Pruys and Klaus Mertens.

[18] The concert of 2011 was Handel's Messiah, with soloists Katia Plaschka, Andreas Scholl, Ulrich Cordes and Markus Flaig.

Every other year, in the spring, the Idsteiner Hexenmarkt (Witches' Market) is held in the castle and palace area, an event with medieval crafts and entertainment.