been given tours of part of the route. This section is found from Patrick Street, where the river ran in two streams, overground for centuries, and then underground until the 1920s, when a single brick-lined culvert was constructed under the eastern side of the street. Having passed through a chamber (7 metres by 3 metres), the Poddle enters Dublin Castle under the Ship Street Gate, runs to the Chapel Royal, and then is turned sharply towards the Liffey; it is in this area that the Black Pool once existed. The Poddle leaves the castle complex by the Palace Street Gate, with a bigger branch line splitting off towards City Hall (formerly the site of the Nunnery of St Mary Le Dam), turning to run parallel under Dame Street, and later angling east. The more direct line continues almost directly towards the Liffey, passing under the Olympia Theatre (formerly a music hall). Beyond the theatre, near the Project Arts Centre, the two branches re-combine and proceed almost directly north, under offices and the quay road. The river's tunnel passes multiple sewers in this area; none normally outfall into it but there are some storm overflows. The confluence of the Poddle and the Liffey is visible at lower tides as a grated opening in the Liffey's stone walls at Wellington Quay. Roles in Dublin 12th-13th century situation The Poddle was used as the boundary between two major land grants by King John as Lord of Ireland, one to the first Anglo-Norman Bishop of Dublin, John Comyn, from east of its original course as far south as Harold's Cross, and the other to the Abbey of St Thomas à Becket, west from the Poddle and as far south as Kimmage. The abbey also held lands further south in the County of Dublin, including a weir on the River Dodder at Balrothery near Firhouse. The abbey is believed to have built the Abbey Mill Stream diversion in that period, changing the flow's direction at a location around the present-day gates of Mount Jerome Cemetery, so as to supply the monastery. However, the supply (especially the persistent dry weather flow) from the then 13 square kilometres flat catchment area was limited and had to supply tenants of both abbey and cathedral, so in the early thirteenth century, they developed a scheme to take water from the Dodder at their weir, by the 3 km Firhouse-Kimmage