Encyclopedia of the History of Arabic Science Volume 3–20 TL pdf

ENGINEERINGThere are frequent references to pontoon bridges in the works of Arabicwriters. They were very common in Iraq for crossing the two rivers and themajor irrigation canals. It is worth mentioning that, to the irrigators, themain purpose of any kind of bridge was to prevent people and animals fromdamaging the banks of canals when fording; the convenience of travellerswas a secondary consideration. In the fourth/tenth century there were twopontoon bridges over the Tigris at Baghdad, but only one was in use; theother, having fallen into disrepair, was closed, because few people used it.Ibn Jubayr, writing towards the close of the sixth/twelfth century, describeda bridge of large boats over the Euphrates at Hilla. It had chains on eitherside ‘like twisted rods’ which were secured to wooden anchorages on thebanks. He also mentions a similar, but larger, bridge over a canal nearBaghdad. There were also pontoon bridges on the rivers of Khuzistan, theIranian province adjoining Iraq, and on the Helmand river in Sijistan (nowwestern Afghanistan). There seems to have been a pontoon bridge at Fustأ¤t(now Old Cairo) in Egypt for many years. In the early part of thefourth/tenth century, al-l$takhri says that one bridge crossed from the cityto the island and a second bridge from the island to the far bank of theriver. About two centuries later, al-ldrisi describes the same arrangement,adding that there were thirty boats in the first bridge and sixty in the second.Before the introduction of modern materials the masonry arch providedthe best solution for the spanning of watercourses and other obstacles. lthough they are relatively expensive to build, well-constructed archbridges can last for centuries and they do not interfere with river tramc tothe same extent as pontoon bridges or the many piers of multiple-span beambridges. Their durability is proved by the survival of many medievalbridges, intended only for the passage of people and animals, but now sus-taining the full load of modern traffic. any Roman, Hellenistic and Sasanid arch bridges remained in use in theMuslim world, and the more impressive of these are described in thewritings of the Arabic geographers. The Muslims, following the traditionsof their predecessors, also built many fine arch bridges. In areas where goodbuilding stone was not available, notably in parts of Iran, the bridges werebuilt from burnt bricks, but most of them were constructed from cut stone.The geographer al-Qazwini (d. 682/ 1283) has left us a graphic descriptionof a great arch bridge at the town of Idhaj in Khuzistan; it spanned a ravinethat was normally dry, but in times of flood became a turbulent lake. It wasbuilt by the Wazir of the Buwayhid Amir al-Hasan (d. 366/977) who con-scripted craftsmen from Idhaj and Isfahan. The bridge was 150 cubits inheight and consisted of a single arch, strengthened with lead dowels andiron clamps. The slag from iron workings was used to fill the space betweenthe arch and the roadway. Another remarkable bridge, over the River Tab763