In average, the medieval streets are found some three meters below the present streets. Archaeological excavations have shown the oldest streets were covered with wood, the oldest being the three layers of wooden pavings found under the northern end of Västerlånggatan from around 1250–1300. During the later part of the 14th century, the streets started to get paved in stone, and as the archaeological deposits above them are composed of thin layers of filth containing few findings, street cleansing was apparently improved during this era. Waste and garbage was often simply poured out into the alleys, occasionally through apertures used exclusively for the purpose. Though a few assumed medieval subterranean wooden tubes and vaulted underground chambers have been found, relatively few traces remain in Stockholm of the sort of sophisticated system of sewers found in for example Visby and Bergen, so most likely the sloping alleys simply had to do the job. Many public notices were in vain devoted to restrain the habit of littering the surrounding waters and restricting the number of animals kept within the city walls, and not until the end of the Middle Ages were gutters ordered to be cleaned twice a week and the placement of bogs forbidden next to neighbours and thoroughfares. Latrines were gathered on central locations known as "flugmöten" ("fly meetings") where the number of insects darkened the sky well into the 19th century.